I know 15-round magazines are made for the compact variety, which is only slightly smaller. Are unmodified 15-round magazines available for the full size PX4 (which is normally 17 I think)? If so, will Beretta swap new 17-rounders out for them?

Beretta will not swap out. If you're buying new, you have to buy with 10 rounders. You can buy 15 rounders after the fact.

 

CDNN has them:

http://www.cdnninvestments.com/bepx49mm15bl.html

Shoulda gotten the .40 S&W PX4 full - fifteen rounds, no waiting.

I love my Px4 inox 40. The magazine are 14 rounds.