There are infact 2 magazine types for the FN-FNP45, one which can hold up to 15 rounds and one which can only hold 10 rounds and which is mostly available in places where local gun restrictions do not allow magazines with a higher capacity than 10 rounds.
Here's the wikipedia link, it provides the different magazine sizes for the different FN-FNP models in the box on the right side of the page.
http://en.wikipedia.org/wiki/FN_FNP [^]