Just picked up my PA-15 10.5 pistol yesterday. I decided to disassemble it today and the back pin was simple to pop out, but the front pin was different. It looked as if was meant to stay assembled and not simply popped out. In any event, I left the rifle hinged, pulled out the charging handle and bolt assembly group, wiped a little CLP around and reassembled.
But, I would like to completely separate the upper from the lower at some point. What is needed to break free the front pin?
More ooph.
And some lube.
What @SuperPredator said. Do it about 15 times and it will loosen up.
The detent on the front pin just needs to have the point taken off little bit. Wiggle the upper while trying to work the pin out.
welcome to the forums @nanney1
your problem will be solved if you do what these fellas say… i’ve also found its best if you have trouble to get a plstic dowel or wooden dowel and tap on it to push it out once you’ve lined it up with the pin. once the upper and lower are seperated i’d grab some lube, put it on the take down pins, go sit down in my den with the lower and lube, put on a good tv show or movie, and just work the take down pins in and ou and in and out while youre watching the tv/movie. by the time the shows over, both pins will be working flawlessly. 
Quick Reminder: field disassembly can be expedited by use of a “tool”. A cartridge is a tool……