If you do replace the sprockets Martin go for a few extra teeth on the back sprocket rather than 1 less on the front, it's kinder to the chain as it doesn't have to go through such a tight radius on the 15 than a 14.
having said that I fitted a 14t front on my Multi (cos it's so much cheaper when you're not replacing the whole set) and although it's knocked quite a few mph off the top end (which you can't happily use on such a naked bike anyway) it's worth it for the improvement around town and the extra acceleration
