I use a Macbook Pro laptop and connected monitor; Since upgrading to OS X El Capitan, Photoshop CC 2015 does not resize its window area when unplugging the computer from the (larger) monitor - meaning all the toolbars palettes are outside of the viewable screen real-estate.
This happens with the Application frame on, and the only way I can see to solve it (ie get it to resize to fit the laptop screen area is to save all current docs, quit Photoshop and relaunch it, wherein it will fit to the new size.
Resizing the laptop screen res in System preferences doesn't make a difference.
It didn't do this in Mavericks - the application resized itself perfectly - but I don't think it's the OS as other apps seem to cope fine with on-the-fly screen size changes.