Charging at 15.1 volts. Anybody?

The regulator should catch the high voltage and shut off the alternator. Did you check voltage at the two field wires in the back of the alternator? Also as mentioned, make sure the regulator has a very good chassis ground! You might try running a good jumper wire from the negative battery post to the regulator and then checking output voltage to see if it will change. Do you have the old regulator?