Yes, the threads are the same. I just canít verify, because Iím not taking my P15 apart, that the ID of the tubes and the depth of how far in the threads are cut are the same. So if it were me, I would get a P15 fill port plug just in case. I built a long tube PP700 for my brother-in-law but I just made the tube and cut everything to fit the stock PP700 hardware. My gut tells me your PP700 plug will work and seal up fine in the P15 tube but donít hold me to it.