Possible electrical issues in my 64 wagon

So I'm having an issue with my 1964 Plymouth Valiant with a 225 slant 6. Occasionally, it doesn't want to start, no click or crank at all. Other times it will start like there is no issue at all. I've replaced battery, starter and ignition coil (today)to this point. I hooked up a multimeter today and checked battery voltage while running and it registered at 15 volts! Could a voltage regulator cause the car to not start?