There've been many models over the years that have been split into submodels to get around the index limits. It is my opinion, one which I have very lightly but not rigorously tested with actual performance profiling, that this makes collision detection slower than if there was a single submodel with all that geometry. When 22.2 comes around I think it would do the general performance of the game good if people, particular the FSU, went in and merged all such models back together, something that the GLTF import/export and blender makes a piece of cake.
Note, I'm not talking about detailboxing. If you have detail boxes that is likely good and you should keep them.
Also, merging everything together should make using the collision LOD options in the ships table easier, and performance would be helped by that too.