Hi Ruud,
the limitation is the size of your RAM - from the number of tris you say it is willing to do, it sounds like you have 8-16. With my 32 GB, I can do around 35 M tris.
It might help if you tell RC that it shall preserve the individual parts duing simplification - I can’t look for the exact phrasing because it’s aligning right now. Other than that, you can set the Minimal Distance Between Two Vertices in the reconstruction settings. The last option would be to split up the model manually…