I would say ask the inspector, but as you are one, that sort of kills that. It comes down to a judgement call. How open is the ceiling? Where's the fan (if it exists)? What is the use (a shower room for a high school gym may require shower trim at 15')?
There is no one size fits all answer. I am currently doing a small commercial design where the shower light is just outside the stall and I (as a designer) still feel it requires the shower trim due to location, as an inspector, I would have to pass the same design with a damp listing only.
I have seen my bathroom ceilings dripping after one of my sons have finished their shower, thus my design criteria.
