The easy "rule of thumb" is you want 10lb's of pressure per 1,000 rpm. 15 sounds a little low, but as long as it climbs and stays above the engine RPM, should be good (famous last words....)
I just noticed all your cars listed... Only problem I see is not enough pontiacs.....
Sorry for being off topic, but I am in the process of talking my father out of a 65 GTO, and 2 '61 Bonneville Convertibles (all needing decent work). He has an extensive collection of over 140 cars last count.
