Doug, you have over-carbonated the beer due to the 20 PSIG. Once you have over-carbonated the product, you have basically lost the last 1/4 of the keg due to the beer is like champagne - full of gas!. Major concern is the 15' vertical rise (vertical distance between the bottom of the keg and the faucet?)and dispensing 40'. It is very difficult to accomplish this with just CO2. A tendency is to increase the pressure to compensate for the pressure drops in the system. This can not be accomplished.
The pressure using CO2 must always be contingent on exact temperature of the beer, carbonation recipe level of the product and elevation. Never use the CO2 to control flow speed or to compensate for temperature fluctuations downstream from the keg or for high vertical lifts and long runs.
If the standard 35' trunk-line is 3/8" I.D. barrier (vinyl/poly???) and the seven feet of constrictor (choker) is 3/16" I.D. vinyl, with the 15' vertical rise and misc. hardware you have approx. 30 PSI of restriction/back-pressure in the system. You would have to push the beer with 30 PSIG to acquire a 128 oz/min flow.
My immediate recommendation would be to invest in a blender and push the beer with 60% CO2/40% Nitrogen at about 25-28 PSIG. Or, move the kegs closer to the faucet.
Scott Zuhse, Instructor
Micro Matic Dispense Institute