Render Time Issues with 300+ 3D Layers Project in After Effects

after effects is for light editing of maybe a few seconds of footage, a minute max with light or spotty effects. anything else and it will chug. There are tests to check your computer's render speed, and they usually take several minutes just to render a few seconds of text and warping shapes. add to that AE really is not ready to be a 3D program...
you should be using Nuke for that one. it's made in such a way that it can actually output something like that, and for me AE has always been slower than nuke, davinci fusion, and even blender's compositor for as long as I can remember.

How long is your comp? Are you trying to edit a sequence instead of creating a shot? The average shot in a movie is less than four seconds. AE is not a video editor. Split things up. It's safer.

I follow the lead of Pixar, Sony Pictures Visual Effects, and Disney. I don't edit a sequence or a movie in a 3D, visual effects, or compositing app. I use those apps to create shots. Almost all of my AE comps are less than four seconds long.

I sometimes have projects that take two or three minutes to render a frame. If the render time starts climbing past that limit, I redesign the shot or pre-render some of the components (the layers or nested pre-comps) and pre-render and replace them using the Composition menu.

When render times start approaching a minute a frame, I always render image sequences instead of video, so if I get a failure, I can pick up where the render fails. Rendering image sequences also lets you change ten frames in the middle of a shot that the client wants to modify instead of re-rendering the entire shot.