I checked that they were critical successes since I modified my stats.Just to clarify, you are getting normal successes -- not critical successes, correct? It doesn't trigger on a critical success ever.
With a 15% chance, you can reasonably expect a trigger every 7 normal successes. You need to get at least 15 normal successes to have a 90% chance of seeing the scene. Runs of over 30 normal successes without triggering the scene should be rare (<1% of the time), but not unheard of.
Do you know what stats modify profession successes, please?
Reasoning perhaps?