WIth your InDesign subscription you can choose CC 2015, CC2014 and/or CS6, choose one of them or run all of them.
What is your OS?
I actually meant to previous update of CC2015, but CC2014 will be fine for my needs (if it's any more stable on this user account). I did consider it yesterday then forgot about CC 2014
Looking at removing prefs now.
If only I had time to trouble shoot this issue. Another all nighter coming up, thanks Adobe.
You can save your CC2015 documents as IDML versions that then can be opened in earlier versions (down to CS4).
Any fully updated subscription version of ID with internet access should be able to use the on-the-fly web-based conversion utility to open the .indd files from a newer version.