I have been on a very long journey getting old MathCAD 15 files in our filestore converted into MathCAD prime format. I thought that the journey had finished a long time ago but discovered more files recently. As MathCAD 15 was centrally licensed from a server and this server has now gone, I was hoping the community / PTC would help get me a temporary license for 15 to allow the converter to work.. We are fully licensed (only two) for MathCAD prime and I find the converter requirement to have the old and the new products licensed a really painful experience. Thanks for the help in advance.
I can't help with a MC15 license but you may want to know that the current versions of Prime are already(?) self contained - there is no need for an extra installation of Mathcad 15 to make the converter work.
But there may be troubles if the MC15 worksheet contains collapsed regions, especially if they are password protected. As far as I know the Prime converter still is not able to handle this and you would need a MC15 installation to open the worksheet, unprotect the region and save it again.
Starting from the 7th version of Mathcad Prime you can use the built-in converter (before the installation process, it is necessary to select it among the installation components).
In addition to the legacy converter, Prime 8 can generate an HTML image of your old worksheet.
The converter is 'pretty good', but some constructs get changed in an incomprehensible way and you won't recall what you'd actually done. The HTML generator will remind you of your exact worksheet and you can edit the converted worksheet intelligently.
Do give regard to the hidden/collapsed regions that Werner_E warns of.