Cooling System Pressure Tester Readings and Input Pressure?

[SP3]

I have searched prior posts on testing the system for leaks with a Pressure tester. For an R-16 car that has 7 pound caps, I am seeing recommendations of pumping up to 13-15 pounds. The tester has markings saying not to exceed your caps pressure in testing.

Confirming, should I pump up to 13-15 psi? Also how long should the tester hold then pressure reading? I initially had a seeping air sound at the water tower and Tester would gradually decrease from 7 psi.

I replaced gasket under the water tower cap and tightened 4 bolts securing tower. The seeping air sound ceased and it held the 7 psi reading longer but eventually it started decreasing (over 5-10 minutes).

Is this normal or in theory a system that has no leaks should hold the Tester pressure without drop until it is manually released?

[Nissanman]

From Google: -
Pressure testing cooling system
"How long should cooling system hold pressure?
It depends, if the engine is warm 1 psi drop every 3 minutes is considered normal (the pressure will drop as the coolant cools) if the engine is cold then it should hold for 10 mins or more."