D4M,
Just me again. Your dealer should be able pinpoint the correct prop pitch and dia. for your 115 Opti. to get max performance. Since Tracker only uses Merc. this should should already be in their books! The only thing that I would add is, make sure that you spend the extra money and get a stainless steel prop. The first little thing you hit, either bottom, rock, floating wood etc. you will have paid for the difference in cost. Plus, there is a slight performance difference as compared to aluminum. Sound like you are getting a nice boat, don’t scrimp on the screw!