The 16 tooth raises the effective gear ratio. First gear in particular is longer and will get you comfortably through intersections without a second gear upshift. The bike cruises easier at 60 to 65 MPH. Theoretically it should have more top end with the 16 tooth, but the motor runs out of torque before you get there. I find the bike runs a bit more "relaxed" with the 16 tooth.
There must be a rideability fine line at the 15 to 16 tooth point, as I think Suzuki could have gone either way. Also remember that one front tooth = 4 +/- rear teeth, so you could split hairs if the correct sprockets were available.
It's cheap to do. Some like it, others don't.
