Having the same problem, for the third year I'm thinking about switching and couldn't take a leap. Mathcad 15 is really nice tool for engineering studies, how it handles units is really great but the mess they made with Mathcad Prime is dissapointing. I'm still waiting and not willing to transfer hundreds of problem solutions into prime, mainly because conversion is not good so I'm in a loop and hope they will keep Mathcad 15 until prime has at least same functionality as Mcad15. Also all my teaching materials are based on Mcad 15 and redoing it... hm, don't really want to. When they get it to be better than 15 I'll be first to switch.