There are posters and sex toy props. But real NSFW is for the 2nd and 3rd ending (for 100% completion and under 15min total, respectively). Those are not subtle at all
The strategy is to simply remember where the keys are and which way to the continuation/exit, and then just beeline there, after having started with full ammo.
I managed to get to about 2min on the first two levels this way, and then third one was pretty much automatic by me just not exploring
