[Steve Kurtas]

So I think I have figured out a solution to the terrible preview playback frame rate of aftereffects 2015.
Step 1: Press the 0 button to preview your highlighted section.
Step 2: The KEY is that you must not see the timeline slider moving through time in your layers panel. If you can see the time line moving, aftereffects will play back slowly. If you zoom in to a different part of your comp (so you can’t see the time line moving) or maximize the comp preview window (by pressing the tilde key) aftereffects will play back at full frame rate.

I am running a new iMac with good specs. But I hope this applies to others. I couldn’t even play a sound file on my mac without the frame rate dropping to half speed. That is when I figured out that if I couldn’t see the timeline moving it would play smooth. The ram preview works exactly as it did in previous versions when pressing the 0 key. You just have to avoid seeing the time line slider move. Hopefully this glitch will be fixed by adobe. It seems like a really easy thing to fix.