If the filter is before the pump and the filter was plugged the pump would caviate and you would loose pressure and flow
take your gauge and run it into the fuel rails that go into the front and back of the carb and see what happens.
also if u have liquid filled gauge drain the fluid out of the gauge as the fluid is glcerin if i know how to spell and fuel gauges are recommend dry to read probably
if you really had 15 psi at the carb your seats and needles wouldn't seat and you would flood the carb as they are designed for 9 psi
Like i said the gauge and mounting location has to be the problem, or i could be wrong but i would try it