How I set up dual monitors on 2015 MacBook Pro 15 inch: I bought two Thunderbolt 3.0 (Mini Displayport) to HDMI adapters from Amazon Basics and two Amazon Basics six foot HDMI cables. Specifically, the adapter is AmazonBasics Mini DisplayPort (Thunderbolt) to HDMI Adapter. I could maybe have used the HDMI port that is available on the right side of the MacBook Pro directly, without the second adapter, but I wanted both cables coming out on the same side of the MacBook Pro; the two Mini Displayports are on the left side of the MacBook Pro. I plugged both Amazon Basics adapters into the two TBolt ports on the MacBook Pro, then the HDMI cable from one to the first monitor and the other HDMI cable to the other monitor (i.e. both are set up independently). Boom, both seen in the display setting the MAcBook Pro. No problems. No hiccups. I could arrange, change scale, etc., from the systems display setting. They both work in 1080p resolution. Specifically, the ideal resolution for these monitors through HDMI cables in portrait mode is 1080x1920 60Hz
Note: the newer version of this monitor is the Dell Computer Ultrasharp U2415 24.0-Inch Screen LED Monitor, which has a higher resolution, I think. I do not know if that one goes into portrait mode or not (description says turns "90 degrees", but whether it does that smoothly in both directions, etc., I don't know (must turn in both directions so that one monitor can have bezel-lee top against the other monitor's bezel-less top (which means it's turned the other way, if that makes sense)). Bottom line: I didn't research that monitor fully, and did not want to spring for the higher resolution (which would make my icons and text even smaller at max setting than on this monitor, which is plenty small enough for my eyes...lol). You might want to other monitor so research it. :-) The resolution of the xx15 model is In-plane switching, anti glare with hard coat 3H: Optimal resolution 1920 x 1200 at 60Hz. But, there are several smart reviews that say modern HDMI cables are limited to 1900 x1080, which is the XX14h monitor reviewed here, at least with the cables as I have it set up. I'm no guru, no idea if all that's true. :-) I also note that this xx14h computer has item weight Amazon under 8 pounds, and the xx15 model has item weight over 14 pounds! Don't know if that's the display alone, or if the box has a ton of packing material...lol. If it is heavier by 45%, I don't want it. Again, YMMV.
Note: I use Amazon Basics USB-powered speakers, which require the 3.5mm headphone jack and a USB port. I can attach them either to the MacBook Pro itself, or to the back of one or the other of the monitors (the monitors each have the necessary jacks). These monitors do not, in and of themselves, have speakers. The reviews of the Dell speaker intended for these monitors was marginal, so I went with Amazon Basics USB-powered as I didn't want another AC cord to deal with. Had I wanted better sound and an AC powered unit, I likely would have bought the Bose ninety-nine dollar jobber, Companion.
Daisy chain: I didn't even bother trying daisy chain the video monitors themselves after reading the nightmares in these reviews. I fretted whether these would work with two HDMI cables, but in the end, it was a plug and play solution. Simple. I'm glad I tried it. For anyone considering daisy chaining these monitors, search these Amazon reviews with the words daisy chain and it'll have you considering the method I used. LOL That said, I think that without daisy chaining, I cannot watch a full image that takes up both monitors...i.e. a gigantic picture. I can mirror both monitors to have identical stuff, or I can have them each act as separate monitors (but with a shared cursor arrow moving across each, from one screen to another). So, when I "full screen" a window, it fills its monitor, but not the other monitor. I can have two full screen things open at the same time--like a Youtube video in one, and an Amazon shopping in the other, for example. I often have a Pages doc in one, and a Word document in the other (portrait mode truly shines for that). However, since I have independent HDMI to each, I cannot have one giant continuous display for movies, gaming, etc. (I do not see a setting for that, anyway, in Display under System preferences, arrangement; someone can correct me if I am wrong). So, if that's your desire, you are going to have to wade into the mucky-mucky of the daisy chaining quicksand. Personally, although the bezel is thin, I don't think I'd enjoy watching videos with the thin black line splitting the screen anyhow. But, that's me. I'm cool with, for example, putting my Tweetdeck on one monitor, and watching Youtube videos on the other, all controlled with one mouse and mouse cursor, if that makes sense.
I added the "Display Menu" app by Thorsten Karrer in the Mac app store, free, which gives me more choices for scaling and puts an icon on the desktop for quick changes in resolution. See it in the Apple App Store. It's use is optional, though. I just wanted more scaling choices depending on the type of work I'm doing (i.e. if I need more screen real estate and windows).
I use both monitors in portrait mode, which works great for YouTube commenting, Twitter feeds, and longer documents. Thin bezel allows no significant "knife" between the monitors when each is showing it's own material (the "knife" might be too much if one is daisy-chaining these babies to watch a movie half on one, half on the other, though). I have read about people placing gaffers tape in the rear to "join" the monitors such that light does not come through the gap between them; I have not found this necessary. All settings to rotate the images to portrait are in System Preferences, Display, Settings. I honestly adore the dual portrait set-up. (One funny finding is that, for some reason, Youtube video pop-up ads--those annoying rectangular things we have to click to turn off--come at the bottom of the portrait page, not in the video, so no more clicking! That said, the video itself is in the center of the portrait monitors, and only you can tell if you like it that way).
IMPORTANT: I watched some Youtube videos reviewing this monitor to discover-- thankfully, before I ordered the two I own-- that the dual stand option from Dell, the one that is offered as an option when buying two of these monitors, DOES NOT allow the monitors to be used in portrait mode! Only in landscape mode. So, anyone who wants even one monitor in portrait, or even occasionally wants portrait, should not buy the stand. Frankly, unless someone is trying to place this setup on a miniature desktop with a single footprint, the stand is not necessary. With the optional dual stand, you won't be using the innate rotating stands that already come with the monitors. :-( So, I did fine (and saved $80) by not getting the extra stand, and now I can choose landscape or portrait, or a combination. The twin monitors sit nicely on my desktop, no issues.
I am very glad with this purchase. If I run into monitors dying, dead pixels, etc., I'll update this review. Dec 6, 2016. The picture quality is quite decent, the set-up was much easier than I had anticipated with my 2015 retina McB Pro.