I have recently ungraded my OS to El Capitan and also have the latest version of AE (220.127.116.11)
I am working on an a imac I purchased recently.
Retina 5k, 27-inch, late 2014
4 GHz Intel Core i7
AMD Radeon R9 M295X 4096 MB
Since upgrading my AE and OS X preview is not able to play back Fps in realtime, no matter how many passes it makes.
I have read all forums on this matter and tried everything I can think of, including uninstalling AE and re-installing.
This issue makes AE un-usable for me as often the playback drops to 13fps (25) making accurate animation impossible.
Audio is also effected.
Thanks in advance,
Exact same problem.
I just got same Imac (late 2015) and due to not having GeForce it means i get about 14fps after its passed once.
I bought this with the optimism of working faster :/
hopefully theres a way around it to improve speed.