I don't have a P15, but I can tell you why I have my '51 and '52. My '52 Cambridge is identical to the one my father bought new. I came home from the hospital in it, and have many nice memories associated with the car. We traded it in on a new '65 Dodge Coronet 440.
The 1951 business coupe is also a reminder of my childhood. When I was very young, there was a dairy company in the town where we spent our summers that had two of them, one in light gray and the other a black one like mine. So when this car came along, I grabbed it. Being one of those 'tow it out of here and it's yours' deals made the decision to get it that much easier!