Pain 15 months post op face/neck lift - Is there imaging or a test to confirm the internal sutures dissolved fully?

There are no imaging studies. Sutures are too small to be detected. You can ask your surgeon if there are any permanent sutures in those areas and name if the suture. In general, the soft braided permanent sutures like merseline do not cause persistent pain, unless a granuloma was formed but that would be obvious to your doctor. The monofilament dissolvable sutures like PDS do not cause pain. Over 10 years ago, I did revise another surgeons lift who used a permanent monofilament prolene suture and this caused terrible pain for months. If it's not the suture type, you might be developing a myofascial pain syndrome like fibromyalgia which has no distinct cause and might be treated by a pain specialist with possibly a med like lyrica. But make no mistake, if fibromyalgia is diagnosed, it is not caused by a facelift...only that your body had that develop concurrently.