Even though I havent pressure tested my car in a few months, I can still get 15psi. It just wont hold for a while. Once in 5th gear it was holding at 15psi for about 5 seconds then would just drop off to 9psi suddenly and not go back up. Then the next pull would be 15psi again. Also some gears are different, sometimes 8psi, then also 13psi. Not consistent.