If you have the 2015 installation files, ensure your hardware meets these specific standards for that era: Autodesk Account Basics | Previous Product Versions

You must possess a valid academic email address (e.g., @yourcollege.edu ) or be able to provide proof of enrollment/faculty status.

No. Inventor 2015 cannot open files saved by Inventor 2016 or later. You would need to export from the newer version to a neutral format (STEP, IGES, or SAT) and then import.