If it starts and runs most of the time, I'd think one of 3 things to begin. In my very limited experience, submersible pumps are either good or bad, not much in-between.
Bad breaker? Even though it's relatively new...I had one fail here at the new house after just a few weeks. If you don't have a spare, swap it with another in the panel. If your well house has an outlet off that 15 amp circuit, or you are comfortable enough splicing in a wire, put a load on that circuit for a while...like a 1500 watt space heater. BTW, you did replace it with a "normal" breaker, not ARC-fault or GFCI?
Next thought is a short or worn wire from the well head to the pump. Vibration/movement makes it short and trip. But...you did wiggle the pump wires. That may or may not change its behavior.
Last thought is a nick or voltage leak to ground in the panel to well underground wire. Put in any fence posts lately?
