You can rent a mechanical oil pressure gauge for a few bucks at many parts store.
Unscrew the oil pressure sending unit, install the gauge with the proper adapter, then compare what you get with the mechanical gauge to your dash gauge reading.
That way you'll know for sure, as it is possible there is some inaccuracy between the oil pressure sending unit and the gauge.
But even if it is 18 psi at hot idle, that is still okay and you shouldn't worry.