Ok so, there should be no limits to how many tris the engine imports but they need to be Tris.
In other words, you should always add a triangulation modifier and export your models with those applied when attempting to import into any engine.
Blender will be able to triangulate almost instanlty.
The engine will attempt to triangulate, but take loads of time to do so, and possibly crash (as experienced).
That said, even for a car manufaturer those numbers are rather extreem…