15v is high, but it's charging, so that's good.
If it runs high all the time then it will boil the water out of your battery, if it puts out less volts as the battery increases, then it's OK. I'd leave it alone and see if it acts up. I like to put the one wire self exciting alternators on mine and ditching the entire external regulator and other two wires for internal regulated, but that's just me, less wiring is better. If you want stock, it's fine. Get a new voltage regulator and try that if you think it's a problem.