Does it open in CC 2015?
CS6 is part of Creative Cloud. Install it and try to open the CC2015 INDD file.
You should get a pop up offering to convert it.
Hi Peter, No. it doesn't open in 2015 its just a blank document
Not sure why it wouldn't be converting correctly if it gives you a file at all.
How about Bob's suggestion to install CS6 at home, too? In the long run, if you need to work in CS6 at school you're going to be better off sticking with that version for schoolwork at home, too, rather than always backsaving.