yamaha 150 4-stroke prop?

[HatTrick]

I just brought my 1986 20 ft home wth a 2005 150 Yamaha 4-stroke. Yeehah! The prop is smaller than the one I had on my old motor. OLD: 1986 merc 150 -15x17. NEW: 2005 150 4-stroke Yamaha -13x19. Does this sound correct? On the Yamaha website they test a 21 ft seaswirl with this motor and use a prop that is 15 1/4x15. Props are all aluminum (I hit a lot of rocks while I fish shallow). What do you experts think? Do I have the right prop?