What size prop?

I am still working on the ignition of Mercury 150 hp BlackMax. So I havnt tested this prop yet. I noticed that there is a 15 1/4 x 15p prop on it. I was wondering what you guys run? My 17' Chris Craft ran a 17p prop with 120hp I/O. It just seems like the 150 Merc should have a 17 or 19 pitch prop? Any thoughts?