There is no free version of MC 15. Programmers want to be paid for their work. But PTC sells a cheaper student license for educational purposes only.
Then there is a (of course free) 30-day trial version which you can download from PTCs website, but naturally it will stop working after the trial period.
Maybe your school/university offers even more discounted or even free edu licenses (then they pay for you) for its students, you'll have to check with your edu organisation.
