Well i have had it on thr 15t sprocket about a week. Will NOT hang with my buddies who have the stock 14t. Off the start and long run. Wont hang. Still pop wheelies easy, and not bad to ride with. I personally will be going back to the 14
I don't wheelie but this has been more or less my experience as well.
I recently had my shop install a 15T in the front, and for the first few rides I felt it was quite good, gentle on starts and particularly 3rd gear was much more usable in moderate flowing city traffic.
I finally had a chance to take it on a road with an 80 km/h limit, and found the engine doesn't have enough torque to pull the taller gear. I could only hit an indicated 82 km/h or so, only a little more with an uncomfortable tuck. Maybe a big bore kit would work well with the 15T but I am not keen on going down that route.
Today I took my wife's Z out on the same road, stock 14T I could get indicated 90/91 km/h, 95/96 tucked. But it's fast enough even sitting straight up. I am fairly certain it's not about speedometer corrections either, the stock sprocket feels noticeably faster.
(I like to think that) I am not that heavy, around 145 lbs on a bad day, but I will also be going back to 14T.