Starting a few months ago I've been getting frequent freezes while working in Photoshop CC 2015. I don't use Device Preview, but whenever these freezes occur the Device Preview window is in the process of opening. I must be accidentally hitting a hotkey that opens the Device Preview window, but I can't find any associated hotkey in the shortcuts menu.
I have no intention of ever using Device Preview, so if there is a hotkey I can disable hiding somewhere in the shorcuts menu that's all I'd need.
If it's not happening because of an errant shortcut I occasionally hit, then the Device Preview window is just randomly jumping into my workspace and freezing the application every now and then and this might be a more serious issue...
May I know which operating system are you using?
Did you try updating Photoshop to CC 2017?