i don't have the P5s, and just got the QC15.
they are pretty good at noise canceling, when you turn it on it's like you turned the room volume level down some decibels. it's not completely silent, but pretty darn good. have yet to try it on a flight.
the sound quality is not the best. i use my IEMs or other headphones if i actually want sound quality.
another thing, QC15s need a AAA battery to work, no battery, no sound at all.