IIRC, you are using the term NAT when you really mean PAT. In true NAT, you will have X internal addresses mapped to Y external addresses.
If X>Y, then you may have requests get dropped or mangled.
PAT is 1 external to many internal shifting/translating the port numbers to create a unique channel.
As long as Internal32768, then you should be okay ; you need to reserve a port for each end of the channel. Realistically, most channels will have 80\443 as an end point. On those types of networks, you can get much closer to 65535. Still, a few badly.configured torrent clients can easily exhaust ports and bring the network down with almost no utilization.