Air compressor kicking in after 15 psi drop

Check the compressor itself. Mine was doing the exact same thing. Ended up replacing the compressor

 

Compressor is pumping to 135 so I would have to say it is fine . The governor controls when it pumps and when it doesn't .make sure there is no leaks in control lines.

 

Mine built to 135 all day when it went bad, but mine was pushing oil into the lines and air drier. Hopefully that isn't the case with yours.

 

The air pressure you see in the gauges are from the primary and secondary air tanks. The governor is plumbed into the wet tank which is separate. It probably is dropping 25 psi, but the other tanks are only dropping 15 or so because their inlet check valves are leaking a bit. Any time you have a fast cycling purge, you have a leak in that part of the air system between the wet tank, governor, unloader valves on the compressor, signal line to the air dryer and air dryer itself. The best way to check is to pressurize the line at the wet tank from the governor so you are back feeding the governor, compressor unloader and air dryer and check for leaks. Compressor unloaders is very common. If you take off the air intake to the compressor you will hear air leaking out from the unloader if they are leaking.

 

I second the above comment. Especially after just having the governor replaced, most likely there is an air leak to the unloading valve causing the issue. Air compressors either fail not building enough air, or through coolant and/or oil usage.