This level took me around 1 hour 30 minutes today, but I played it before in the past. The second half is tough. Thats where I spent most of the deaths. I always come back to the game months later and forget the controls so I had to re-learn the game somewhat.
Theres a few spots where you can stand and punch hordes of enemies to death. Two in the beginning and then the rest were improvised by grouping enemies and removing thier guns when possible first. I also left all guns on the ground and didnt use them so that I could save them for the boss. Seems some of them disappeared but it made a huge difference since he takes so many hits. You can bait the boss to charge into the wall after he screams, if you are far enough away when he does it and near a wall. Then you can get in some free hits. Only managed it one time in this run.