Hi sbh - Welcome to PSG! FWIW, I've never heard of any sort of master list or tool to check backwards compatibility of PS actions, and I doubt that one exists because backwards compatibility is going to be extremely dependent on the details of the action and there are so many different PS features that a given action might use, as well as so many earlier versions, each slightly different.
For example, if you read Adobe's description of what's new in CC 2015, quite a few of the menu items have been moved around (eg, "Save for Web" is now listed as a legacy menu item and has been moved under "File/Export"). So, if you develop an action to use the "Export" version of "Save for web", it will be almost guaranteed not to work on any earlier version.
With respect to compatibility of PS actions with Elements, again, I can almost guarantee you that there will be major problems because of the very different structure of the two programs, although I should confess that I don't even own a recent copy of Elements, so I'm not a good guy to ask.
If you are a developer of actions, I think that your only recourse is to keep multiple versions of PS on your computer and develop a compatibility list for each of the actions you develop. OTOH, if you intend to purchase some CC 2015 actions and are interested in whether or not they may work on earlier versions, just ask the developer.
One of our members, Paul MR, is a master of PS scripts and hopefully will see this thread and give his insights.
Cheers,
Tom M