If you want to translate the Mathcad 15 files to Prime, you definitely have to have Mathcad 15 installed, because it is used in the process. Depending on the complexity you use in the Mathcad sheets, you may have alot of correction work on the converted files.
Note that there is no tool to translate Prime files back to Mathcad (.mcd or .xmcd) files. Also Prime 4 cannot save files readable in Prime 1, 2, 3 or 3.1.
Anyway, Success! Luc
Ah, you could even decide to not install Prime at all, just Mathcad 15...