So a few weeks ago I was giving a presentation about video editing in Photoshop CC and something weird happened. I was trying out giving a presentation on my new Microsoft Surface Pro 3 for the first time and curiously my Photoshop interface decided to "upsize" itself every time I plugged it into the projector.
Well I have found the root of the problem. The problem was caused by a preference setting that automatically triggers when it detects that you are using high-intensity displays such as the Microsoft Surface Pro 3. It scales the entire Photoshop interface up by 200%. While the interface looks fine on my tablet during normal usage, it becomes horribly oversized when it automatically down-res itself to clone the projector display.
So if you are also facing the same problem, the solution is to go into your Photoshop preferences, go down to the last section that says "Experimental Features" and uncheck the "Scale UI 200% for high-density displays" check box.