Photoshop is very small

Auto is the problem and Adobe default setting. Adobe for some reason scales UI 200% on displays that should not be scaled.  In this case Adobe is scaling  a 1920x1080 display 2x in effect making the display a 960x540 ui display. Photoshop requirement is 1024x768 Photoshop's UI will not fit on a 960x540  display.  They need to set the Photoshop Preference UI Scale from Auto to 100%.set to set 1x..

So if you have a Surface Pro 2 or 3 Adobe knows you have a  high resolution display they should also know you do not have the reqired number of pixels to support 2xUI 3MP 2014x1536.  Surface pro 2 1920x1080 and Surface pro 3 2016x1440 do not have the required  3MP.  While the Surface pro 3 has more then 3MP its aspect ratio is 3:2 not 4:3 so it effectively a 1080x720 2X display the 720 falls short of the required 768.

CC 2015 is even worse Adobe changed ScriptUI and it does its own Dialog Scaling and does not use Photoshop Scale UI setting. Setting 100% does not help some Script dialogs will not fit on screen when scaled and will not be useable.

In photoshop go to Edit>Preferences>Interface, set the UI Scaling to 200% and the restart photoshop.

I will move yoyr question to the Photoshop forum, this is the Captivate forum. This is probably due to the display percentage on the Surface.