Photoshop CC 2015: Won't save or takes hours to save image

Since I updated to CC 2015, it either crashes during saving an image, or just takes forever to save it. On eimage took overnight. Last image I tried to save took over two hours, Original RAW file was around 33MB and when finally saved was a whopping 450MB Photoshop file, despite having made only a few changes to it.
I'm on a fast I Mac, with maximum memory, tons of space, latest System and have tried restarting and closing all other applications.
Am unable to return to CC 2014, as unfortunately I didn't realise until too late that CC2015 automatically overwrites previous versions, unless you specifically go into preferences and tell it not to.
Anyone else having this problem, or any clues to rectifying it?