Prop question

[EZAKMC]

i HAVE A 83 15HP AND NEED TO BUY A NEW PROP. i SEE YOU HAVE MANY TO CHOOSE FROM. I DONT KNOW WHAT TO BUY (PITCH AND 3 OR 4 BLADE)
I HAVE A 11.5 B***TENDER BOAT AND RIGHT NOW IT SEEMS TO SLOWLY GET UP TO SPEED WITH ONE PERSON BUT WITH TWO IT SEEMS TO JUST PLOW THRU THE WATER. I AM GUESSING THAT THIS COULD BE CURED WITH THE CORRECT PITCH PROP.
IF NOT THEN WHAT PROP WOULD BE THE FASTEST? ALSO WHAT IS THE DIFFERANCE BETWEEN THE 3 AND 4 BLADE?