Voltage Regulator

Those reading look OK. One question...........at what point did you get the "almost" 15V reading? If the battery /VR was still a bit cold it could have been so. That reading is not TERRIBLY high but is getting there

One last thing, this is the 70/ later "flat" electronic VR, right? If so, the connector/ connection at the VR might be suspect, pull that apart, examine, look for corrosion, etc, and "work" it in/out several times to scrub the terminals and to "feel" for tightness

If you can "drum up" a known good battery (maybe out of another vehicle) you might drop that in and be sure the batteries are "up."

If nothing else just "throw the money" and replace the VR. This can happen, but rare