-Previews: - also self apparent - nixing ram preview sounds AWESOME, but clearly it's not quite ready.
-Playhead: on audio preview, it only makes sense for the playhead to return to original position, not end up some random number of frames downstream. that's fine if a spacebar-preview.
-Playhead: randomly sticking to my cursor, sliding around. Also hitting spacebar, sometimes stops it, sometimes doesn't, sometimes goes somewhere you wouldn't expect.
-Sync: maybe editing dialogue it's okay for A/V to be a little out of sync here and there, but in detailed motion graphics, I'd MUUUCH rather wait, than have unreliable or non-instant first-frame sync.
(or at least have a clear option switch "sloppy-quick OR accurate-but-you-have-to-wait")
(sorry, but the "mute if not in sync" preference is just plain weird and useless)
There is an update that is scheduled to come out in the next couple of weeks that is meant to fix a lot of the issues with the new preview system.
I can't afford to buy a dozen new plug-in upgrades.
You shouldn't have to pay for any new plugins. All of the major plugin-makers (and all of the minor ones I've seen) are offering free updates to their plugins for CC 2015. Most of those plugin updates were available on launch of CC 2015 or within the first day or two of its release.
Now, to your main issue:
I downgraded back to CC2014, which works like a charm comparatively, except now all of a sudden, when I'm in output module, if I try to change the codec, it crashes every time.
What format or is it for all formats? You might try uninstalling and reinstalling CC 2014 if it was a recent reinstall.
What about CC or CS6? I have CS5, CS6, CC, CC 2014, and CC 2015 all installed on my machine just in case of weirdness like this or for compatibility with clients, so I'd recommend always choosing to keep the old versions around.