There are several ways to handle this type of thing. A most effective way would be to create a new called something like old_filename_shrink . Use feature>create>data sharing> ext shrinkwrap. Pick the old_filename and use the default csys. Cracnk up the quality if you need to, the higher the number the better the copy but it takes a little longer. This will create an exact replica in surfaces and it will be enormaously faster.
You could then sub this model in. To be better at config management, put the old file in an empty asm and create the shrinkwrap there, then simp rep off everything except the shrinkwrap. This gets it all down to 1 surface featue.