If it genuinely looks to be teeth and I had confidence in the vet, I would do it without hesitation. My previous old boy had a dental at 18.5, we had put it off for so long that it eventually got to the point where it was a choice of risk the operation or have him pts, so we felt we had nothing to lose.
He had pre-op bloods which showed his kidneys were a little (but not a lot) on the dodgy side, so he spent the night on a drip to make sure he was very well hydrated before the op, and then he had the op with all the drugs suitable for older moggies. Not only did he bounce back very well from the op, but he gained a new lease of life. It was only afterwards that we realised how much his teeth must have been bugging him for ages and how much better he must have felt as soon as they were all sorted. His heart murmur also cleared up - apparently bacteria from bad teeth can travel around the body and cause problems in other organs like the heart, so again it's good to get the teeth sorted to help keep the other organs in order.
It's a tough call I know, but with hindsight and seeing how much difference it made to him, I'd have had Sooty's op done sooner rather than leave it until we had no choice. He had another good quality year and a half after that final dental (which left him with no teeth at all!)
Good luck with your little one x