Your check valve is leaking. 15 years is a long time for a check valve. Get your guys to pull the injector and replace the check valve ASAP to prevent your pump, pressure switch and tank bladder from wearing out.
Be careful that nothing gets in the pipes or injector. If the pump won't build pressure after reinstalling everything, some debris got into the nozzle of the injector. If this happens clean the nozzle. Pumps don't build the pressure, the injector assembly does.
By the way I'm 75, I have to get my sons to do the physical work now. . . I just point my finger!