Hi, I just recently bought a new LG 27" 4K display (LG27UD68) for my 2015 13" Macbook Pro retina. It works flawlessly on the max resolution 3840x2160, but text and ui elements are just too small. It also works flawlessly on 1920x1080 resolution, but here everything shows much too large. However, when I try scaling it to something useful like 3360x1890 or 3008x1692 or even 2560x1440, everything on the LG display starts to lag, UI elements lag, you can feel some lag using the browser, photoshop and other programs. At the same time, everything on the Macs retina display runs smoothly even when the LG monitor is connected, same UI elements and browsers don't have any lag. I am running the monitor trough a DP 1.2 cable at 60 HZ. Previously I had a DELL 25" 2K monitor and it ran perfectly on the 2K resolution. Once I even connected two of these monitors and they both run without any issues at all. I have searched everywhere, but cannot seem to find any solution or even explanation for this problem. My laptop runs macOS Sierra 10.12.3. Specs: MacBook Pro (Retina, 13-inch, Early 2015), 2,7 GHz Intel Core i5. I would appreciate any help. Thank you.