That's really annoying!
I'm not Todd, but I do know that a major bug fix update is coming for CC 2015 in less than two weeks (they said "the end of the month"). This update may fix enough bugs to make CC 2015 usable for you.
Until you hear from Todd or someone else who can help (or the update comes out), have a poke around these forums. There have a been a few threads about El Capitan and some of them might help.
May I have your old one for the ministry I oversee?
Just installed the latest updated for CC 2015. Absolutely ZERO performance increase. I can now get a longer ram preview, but it still refuses to play back at realtime. Interface still feels sluggish to me as well. I can't scrub through a simple comp based of illustrator layers with only very simple position and rotation keyframes. It will only show wireframes, even with adaptive resolution turned off (or on, for that matter).
These new machines continue to be unusable with Adobe software.