You got it--the Potter 15 is fourteen feet long. The little Potters have always been fourteen feet long. The earliest ones had removable outboard motor mounts and were listed as 14 ft in length. When HMS Marine began to build them with fixed outboard motor mounts they measured the motor mount too and got 15 feet.
I got rid of my open cell foam bunk cushions when I got my Potter (they were full of mold) and bought a closed cell foam swimming pool float. Its so blue it almost hurts my eyes, but it makes a very good bunk cushion--I've slept on it probably three weeks or so total, and been very comfortable.
Regards
Tom Grimes
P-14 #363 Far Horizon
Muncie, Indiana