I've just noticed that you entered a trimesh into a brep. This is something you should definitely avoid! It takes all single triangles and creates single surface patches which means for many triangles this takes a lot of time. It is a very special functionality - and, seeing your problem, I think we should not allow this anymore (we'll discuss it in the team). It is useful for only a tiny subset of problems.
See the attachment. Before you open your file, deactivate the update process. Then you are able to open your project and e.g. remove the last BRep operation, or set the BRep to invisible etc. Then activate it again to generate the model.
When looking at your project, I guess you want to work on the tongue part (where the inlet and main surface intersect each other). If you need assistance, it is recommended to open up a new post or check existing posts that cope with tongue modeling.
BTW - Just as a side note: For exporting the BRep as STL, you don't need trimeshes. Actually, we do not use trimeshes so much anymore for our projects. There are only very specific situations where trimeshes are helpful, e.g. when your initial situation starts with STL data and you need to pre-process it, or merge a parametric model with external STL data.