So I foolishly ran a dedicated 15 amp circuit to my hot tub using 14-2 wire. Worked well for a couple of years, but then I had to replace the spa motor. The new motor trips the 15 amp circuit breaker about once a month. I'm considering swapping out the 15 amp circuit with a 20. I know this is against code, but it is a dedicated line that is buried about 12 inches deep, also the run is only about 30 feet. From a non-code perspective is there any danger here? I think the spa pulls about 12 amps nominally and then spikes periodically. What's weird is it never trips when I'm using it, even with the jets and the heater on simultaneously. Another weird thing, it's connected to a 15 amp bi-pole breaker, and the "sister" breaker also trips periodically. Another option would be to replace the breaker with another 15 amp breaker. Any suggestions?

That's why I like to run in pvc. Try this, turn off the power and, if the soil is loose enough you may be able to tie on. 12awg and pull back to the box and use a 20 AMp. This is ground faulted? Why a 2 pole breaker?

Thanks, I think I'll just buy some fishing tape and pull through some 12-2 wire just to play it safe. The 2 pole breaker (if that's even what it's called) was put in because my box was getting full of the large breakers so I went with the mini breaker that has 2 breakers but only uses one breaker slot.

Now that you mentioned it was a mini breaker, that's different, it isn't a 2pole,it's a double single pole designed for 2circuits
Go with 12AWG.