I always get this mixed up BUT I think it's the 6600 that's high shank whereas most Janome's are low shank. Or maybe it's the other way around! I have a stickie note at home to remind me of which is which but I'm at work and can't remember for sure.
I have 2 Janomes (a 6600 and a 3160) and one is high and the other is low, and they can't share some feet but they can share others.
If in doubt...find the part number for that foot and look up your 6600 on Janome.com and see if that part number is listed as an accessory for it.
I don't know what foot the "P" foot is, unfortunately.
Or, you could always just test it! See if you can borrow the foot from your friend, put it on your machine (if it will fit) and then hand-crank through a cycle and see if anything hits. If it fits and nothing hits go ahead and do a few stitches and see if everything looks OK.