Resolved. I got a working head which I shot with Polycam, redid the Topology with Wrap4D (or ZBrush, one crashes more, the other less:) ) Then threw in the texture from the original MH and conform and done. It works and the details are great. Although MH tweaks the look of the model a bit about 20% looks a little different, but it can’t be helped, it’s almost 1:1 from my scan. Now I want to solve the photorealistic texture from real photos and then I’ll solve the great clothes 
anyway thanks a lot for the help, I was about to give up the whole UE, GTX 960m is a really old GPU, but no, I just don’t want to give up