For now, here's a workaround to pick up speed -- Download AE CC 2014, and use it to render with Multiprocessing. Unlike the current version that uses only one processor (because Multiprocessing was disabled), Multiprocessing assigns computer cores to work on different frames simultaneously. CC 2015 project files will open in it.
You see, AE's a work in progress. Or in transition. That the nice way of putting it.
Calling a spade a spade, Adobe management has blown off issuing orders to re-work the basic code that makes the application run for... oh, about 10-12 years. Now the chickens have come home to roost, and they're scrambllng to catch up to the point where other applications were 3-4 years ago. One of the casualties in this massive code re-write was multiprocessing, Another was identifying & fixing bugs before release -- recently, bug fixes have created new bugs that never existed before.
Will multiprocessing ever work again? Will it be replaced by another, speedier software scheme? Will the software remain buggy? Stay tuned -- and enjoy paying a monthly fee for the privilege of doing so.
Haha! WIP - yeah, nice way of putting it.
Yeah, I know of the workaround, but come on. Seriously?!
(I actually tried it on earlier projects. But at the time that didn't seem to help an awful lot either.)
I just don't understand why they invest workforce in new features at the same time while this is till a tremendous issue. I know, doesn't sound as good in marketing. ("The new features for AE CC 2016 are ... well, we fixed the old stuff! Yay!") Sure, but frankly, since most people have moved to the CC Versions and nobody needs to be convinced anymore to invest in the newer versions, they could actually focus on fixing stuff. Paying customers would be a lot happier, because they would actually get "more time" and "less stress" as new "features". (I am aware btw that the math in this is a bit crude )
I guess we'll have to see what time brings. ... Or switch to different tools that may arise in the meantime.