@KubeKing What's your process for reducing the map to dev brushes? I'd like to try a similar project, but I'm having trouble doing this quickly.
There's a lot of deleting more than anything. Start from the tops of buildings and work your way down.
The main things you have to worry about are leaks and skybox brushes. They have to be managed with supplemental brushwork, which requires a decent amount of trial and error. Your goal is to get the map's brushwork to be as clean and as simple as possible: always keep that in mind.
Reducing a map to dev brushes is not a 'quick' process by any means, but it isn't the hardest part of making an event map. Figure out exactly what you have to delete and how you must prevent leaks, then go for it.
Pro-tip: It may be useful to take screenshots of detailing you with to delete, and sketch the detailing you wish to create over top.
Edit: On symmetrical maps, you should probably delete one side straight off the bat. You don't want to have to repeat the brushwork reduction.