I performed a 17 seconds time on the elevator boss in hard mode. I think there is some way to repeat it but I'm not sure since I slowed the time in the process. The idea is to begin while climbing the most at the left possible, then to jump on the boss asap. A grenade will be block on the boss and a cable, will glitch in the boss while he goes up, and explode its middle and insta kill it.

I hope this can be useful to someone, I'm not good enought to speedrun but I'd like to find ways to make glitchs work so I'll try to find some other.

I've a screenshot of the final time after the boss if needed :)