They both use nanoSIMs, so yes. (That's the only thing you have to check, and GSMArena has the specs for all GSM phones (and a lot of CDMA phones too).
I believe Sprint is the only carrier where, for whatever reason, you have to physically get a new SIM card activated for use in the 6p, all other carriers just let you hot swap.
Posted via my Nokia 8210 from the inside of a Kitten.
I was able to use my micro sim from my Galaxy S3 with the 6P. I cut it down to size and it worked fine. It was much easier than dealing with AT&T not recognizing the IMEI number if I got a new SIM.