65355 vertices, due to vertex index buffers being 16 bit unsigned ints.

65k plus models are what playstation use. It's to do with hardware and the amount of memory Unity uses. Not sure how/if you can jack it up but it's industry standard (next gen consoles of course) to have around that many. My guess is the model your trying to bring in is super high detailed or turbo smoothed (3ds max jargon). If that is the case may I suggest some retopology, can help bring the poly count down whilst still keeping your detailed model.