It's a bit weird... there's a scaling option in the display settings with 250% being the recommended amount. So when I open a HD Quicktime video, it's bigger than the entire screen, even though it should only take up a quarter. If I set it to 100%, that's what happens... but everything is crazy tiny. You can barely read names of folders on your desktop.
CC2014 is my After Effects of choice, as I've not been keen on the way the panels work in the later versions, but I have to get six inches from the screen before I can read any of the text. The file/edit/view menus at the top are fine as the size of those is dictated by the scaling option I mentioned above, but the main body of the AE window isn't affected so everything is tiny.
So I've had to begrudgingly start using CC2017. It's all a bit crazy, maybe should have gone for an 'old-skool' 1080p one!