Tire fitment conundrum (How bout that for a 50 cent word)

Vehicle: 2013 Tocoma access cab, 2.7 4cyl, 2x4, std tire size 215/70-15. Also truck is used to tow a boat.
Problem #1 Speedo reads (from day 1) +4 mph from actual (gps) speed.
Problem #2 Time for new tires!
Would like to go to a taller tire to correct the speedo, but open to suggestions for fixing the problem. Tire size 225/75-15 is appx 1.5" taller that stock and should pick up about 3 mph on the speedo. Tire manufactures: Cooper Discoverer A/T, Goodyear Wrangler A/T of Firestone Destination A/T. Boat ramps get slick and wet so need a tire that will handle it (also hits the roads in the National Forest).
Thanks for any and all help! aj b

 

Found the right forum for this info! Sori