I have the exact same setup. '53 full pressure engine and a 30# gauge. 10,000 miles since total professional rebuild. The needle stays pegged on 30# until it is thoroughly warmed up. Once it is warmed up it drops to 15-16 at idle. I keep the idle at around 450 RPM. At 600 RPM, it pegs the 30# gauge.
You are fine. Nothing to troubleshoot whatsoever. 15 PSI is twice as much as you need at idle. Oil oozing at the rocker arms at idle verifies this.
Carl

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission