You have CC2015. You say it won’t open your older files but you didn’t tell us what happens when you try.
Is there an error message? What operating system are you using?
Sorry, I meant to say that my older version won’t open the newer version. I had downloaded the trial version (newer) and when we bought our version it is the older CS6 version. We bought it under our non-profit status and got the older version that is not a cloud subscription to save money. I tried to re-download the newer trial version just to save the files as older versions but apparently I will have to install it on a different machine as it won’t reinstall the trial version on my machine. I just figured that someone would have a file conversion tool.
Oh, so you opened the old files in CC 2015, then purchased CS6? You could:
a. Open the original files on CS6 or
b. Find someone with 2015 who can package them for you to open in CS6.
Or or install the trial on a different computer and do it yourself.
I will take the files home and install the trial on my personal computer. I should be able to handle it after that.
InDesign files are not down-gradable. Any data created by a newer InDesign version cannot be read by an older version. You need to export (File->Export) your files under IDML exchange format. To my knowledge, there is no third party conversion tool.