high voltage stock 6.1 alternator

anyone experiencing high voltage if running a stock 6.1 alternator with the oldschool external voltage Regulator? I measure 15V unloaded and 15.5V when headlights on. This is a little too much or? I am afraid of cooking my Batterie. I changed already the regulators ( same type ) but no change at all.
Any idea why the voltage is that high and how to drop this at least 1V?