I just bought a used 1448 Jon boat with a 2003 9.9 two-stroke Mercury. It will be mostly a duck hunting rig for flooded timber in AR with occasional use in the rivers around Knoxville, TN for hunting. Thinking about upgrading to a 15 or 20hp (it's rated for a 25hp max). One, is it worth looking into a 15hp motor vs the 9.9? From what I read you only gain a couple of MPH but the difference between a 20 and a 9.9 is huge speed wise. Guessing the 15 will push the boat better regardless of load compared to 9.9. It is usually just me and my dog. Occasionally, one other adult. Also, I have read you can "upgrade" the 9.9 to a 15 with just a carb change on the older motors. Most of what I have read talks about doing this with a four-stroke, can the same be done with a 2 stroke?