I'm having a big issue with my latest iMac 27" 5k and after effects CC 2015 :
I can't play a video at normal speed, i can't work on my projects which were created with a 2011 old 27" iMac on Yosemite because it's too slow!!
How could it be?
It seems that after effects can't use the power of a new iMac, are you serious guys?
So people, don't take the new after effects CC cause it doesn't work yet with new iMacs.
AE CC 2015 is alpha software. It's not feature complete.
There is no multicore rendering, which is why it's performing so terribly on your Mac.
Go back to 2014 edition, and update the meaning of "update" in any dictionaries in your house.
Put an * next to the word, and at the bottom of the page right this footnote/caveat:
*Update is considered to mean something different by Adobe. They seem to think it means to run an early build candidate via paying customers for testing of issues, bugs and problems. This has been found to be more cost effective than paying testers and hiring sufficient developers to release fully functional software. It's one of the great joys their shareholders revel in with the move to a subscription payment system that removes the option of ownership.