Listen dude, I'm all up for unique fantasy races that seem well put together, especially if sexual dimorphism of sapient races is involved.
Put pray tell me, in what fucking circumstances would you need to explain to somebody how troll reproduction work, no less in so much detail that semen baths are viable answer?
Just make troll reproduction closely guarded secret from outsiders. Like, it's a taboo. The trolls might be pretty chill, but a surefire way to make them angry is to pester them about "how is babby formed, how girl get pregnant".
If you absolutely need it explained, this >>63541476
gorilla analogy will do.