Autoclave Overview
"Autoclaves use saturated steam under pressure of approximately 15 pounds per square inch to achieve a chamber temperature of at least 250°F (121°C) for a prescribed time—usually 30–60 minutes."
All of the autoclaves I've personally had ran at 20lbs, and I'd swear I've seen stainless pressure cookers that will do the same, but according to UCSD a 15lb cooker should work, just run it longer.
If you want to be sure your setup is good, run a spore test kit through. If it's sterile the spores don't grow.
Duo Spore® Biological Monitoring System Test Kit with Mail-In Culture Service