That is a bit odd.
What OS are you using?
When did you first notice this issue?
Has it ever worked before? (If so, what changed? I'm guessing an OS update.)
Have you tried in CC (version 12)?
Have you tried CC 2015? (If you do try it, make sure you don't let the Creative Cloud app delete your older versions! keeping previous versions installed when installing CC 2015 applications)
If CC 2015 works better than CC 2014 in previews, you'll blow some minds...
It's running 10.11.1
I've been on CS6 until now, apart from a trial of CC a couple of times. So it's a new issue with the fresh install of CC2014. I haven't tried CC2015 as, well… you know. But I guess I could do.
With CC2015 it's not as bad, mostly. When I increased OS X retina scaling to maximum resolution, it did slow down to 8fps but then on successive Previews, it crawls back up until it reaches 25fps (realtime) with an occasional slow down to 24 or 23fps.
Interesting. Well, it's good to hear that CC 2015 is better for this. Hopefully after the update (supposed to be here in less than a week), it will work even better.