I have a very newbie question. I have been using After Effects 2015 (ver.13.8.1) and I am about to upgrade to the latest 2018 (ver.15.1). I am in the middle of a project and I want to make sure that I can open all the files with the latest version. Can anyone please tell me if it's compatible? In the past when I made the upgrade from CS6 it was quite a hassle to open the files so I want to make sure that I am prepared if that's t eh case.
Unlike Dave, my studio actually uses Ae CC 2018, so I can speak to it from experience. I'd consider it a big step up over Ae CC 2015.
One big caveat, though: the latest version drops support for legacy QuickTime codecs. Most common production codecs are now supported directly by the Adobe apps, but if you're using an older codec, you should stay on the previous release and consider re-evaluating your workflow going forward: https://helpx.adobe.com/x-productkb/multi/quicktime7-support-dropped.html
Ae CC 2018 should read Ae CC 2015 files without issue. (But this should have been your experience going from CS6 to CC 2015, too. I'd be curious to hear about what kinds of issues you rant into.) Note that you can install multiple versions of Ae side-by-side, so you can test for yourself how well it work by using the Advanced Options in the Creative Cloud installer, and unchecking "Remove old versions:" https://helpx.adobe.com/creative-cloud/help/creative-cloud-updates.html#Adv...