You can run both CS6 and CC2015 on the same computer.
The best workflow would be to export your reflowable text ePub from InDesign CC2015, selecting ePub3 and then convert it to a mobi file using the free Kindle Previewer.
Which doesn't work on a Mac without a terminal hack.
That's not so, but anyway why not upload your ePub via Amazon and let them do the conversion.
The conversion has some bugs. The last page of several chapters that are less than a full page are truncated. A bit odd.
It’s a known bug that Kindle Previewer doesn’t work from a straight install. Got it up and running after doing the hack. In fact, I'm surprised you were able to install it on a Mac without any issues.