Remember that changing dire diameter effectively changes gear ratio so you'll want to keep that in mind. A taller tire lowers the numeric ratio - I have a 3:08 gear in Mutt and 2 sets of tires, 28" tall and about 22" tall. I forget what the calculated ratio change is but it's significant. Going from a 14" rim to a 15" rim probably won't be that drastic but still, it's there. The shorter tires will accelerate more quickly but require more RPM at cruising speed. It will, therefore, throw your speedo off so you'll want to remember to correct for that (I've seen a little chart posted on the speedo with the correct numbers, 50=54 or whatever). There are online correction formulas to help generate the chart.

Dan