I have had a time with these Matsushita 15V motors in Panasonic, National boomboxes. Every one of my Matsushita radios have new motors in them. They all seem to fail the same way. They start running slow usually. You can adjust the trim pot, but they continue to run slower and slower or inconsistent . By the looks of the distortion around the speed adjustment hole, it could also be a damaged trim pot inside. If they fail, the motor will run extremely slow.
I went through 4 of these motors trying to find a used 15V motor thinking that is what I had to use. All of them had speed problems.
Test the voltage at the motor with a volt meter. I am willing to bet it is unregulated and is no higher than 13.3V or less than 14. Most of the time, these 15V motors were used because they were installed in a radio that has Universal Voltage. I am relatively sure a 12V CCW motor with a speed trim pot will serve you just fine in your Panasonic
There are members here who can direct you better on how to know you are getting a good proper motor for your application. I do know that you should avoid the cheap fake Mabuchi motors on eBay. I tried one of those and it didn't work. Aside from those, there are plenty of 12V CCW motors out there to choose from at decent prices.