You can go up one tooth on the front sprocket, or down 3 teeth on the rear. I chose one up on the front because;
1.) Less chain bind (A small front sproket causes more friction 'n power loss.
2.) It'll shorten the wheel base make'in the bike steer quicker, butt it'll be less stable at high speeds. (I don't care, I like my bikes twitchy like my women! )
Good selecting of sprockets HERE
Also when you change the gearing, your check engine light will come on eventually, and gear selector will go crazy. The cure is to jump the clutch switch at the handlebars. See page 15b of this tread, @Boat has a nice pic 'n description.
With the 15T front sprocket, was the decrease in wheelbase VERY noticeable? I would think not. Butt stock wheelbase is perfectly fine, and I don't need it to be more squirrely. Would getting a new chain with an extra link offset this and set the wheelbase (closer) back to stock? I only say this because when I get the Norton power package installed, I feel a taller gearing will be necessary.