Stalled Follicles- Natural FET

Does anyone have any advice or insight for this situation?

My clinic wants to see a 17mm follicle to move forward with a trigger shot. I am at CD12, with two follicles--one at 15mm and one at 16mm. The larger one has been at 16mm with just a little growth since CD10. The smaller one grew over 1mm during that time. Lining is great at over 8mm trilaminar and progesterone is great too. No stimulation this cycle-- just trigger shot followed by progesterone. No LH surge yet on OPKs.

I haven't tracked my temps for a long time but have regular cycles with all the signs of my body gearing up for ovulation. Last cycle I tracked with opks and did get a surge on day 11.

My RE is concerned that the follicles aren't growing faster and thinks it could be due to my age. I am 44. I normally ovulate anywhere from days 12 to 15. We're going to check again in two days to see. She will let me continue if I want but mentioned that canceling might end up being better. My clinic prefers medicated cycles.

Has anyone been successful after stalled follicles, or with a 16mm follicle on a natural FET? Or do you know about research around stalled follicles?