2 days ago the Quick Selection Tool suddenly started running in super slow motion.
I was running PS CS5 until about a year ago when I upgraded to CC2014. I've been running CC2015 for a couple of months now.
I tried a fix that involved Preferences>History & Cache> big and fat. No effect. I changed history states from 50 to 25. Cache levels I set to 4. No effect.
My hard drive is carrying about 33% empty space.
This is the Lightroom forum, you might want to try your question in the Photoshop Forum.