I just got a new MacBook Pro (not the one with the Touch Bar, mid-2015 model), and unfortunately KSP does not support Retina Display; which basically means that a 15" (38.1 cm) screen has a 2880 x 1800 resolution, twice the normal (1440 x 900) resolution of usual 15" screens. This makes the GUI look way too small when played on full resolution, and even the UI scale slider only goes up to 150%, and is not sufficient.