Hi Mike and welcome. Yes, the 10rd magazine is the same physical size as the higher capacity magazines which are just internally blocked for sale in capacity restricted States. The pistol will accept higher capacity magazines no issue. FN does not currently make 15rd magazines but aftermarket has limiters available. Your FFL can order and pin the magazines : magazineblocks.com/magento/products/magblock-kits/pistols/fnx-9-magblock-10-17-10-and-15-round-limiter.html

the 17 round mags will fit and work just fine. I could not find a 15 round mag

Hi Mike, yes sir, not sure if they make a 15rd magazine for this gun, but it will accept the 17rd magazines.
The 10rd magazines are the same size/dimensions, they are just pinned to 10rds for those who live in restricted states.
budsgunshop.com/product_info.php/products_id/62618/fn+476942+fnx-9+9mm+17+rd+black+finish ,
Stay safe & have a great day!