After Effects only using 12% of 32 GB RAM while rendering

Your project is so lightweight you won't see any improvements with a separate pass, but yes, audio processing is mostly linear and AE isn't that good at it. If it really bugs you, rendering only the visuals with multiframe rendering on full throttle and importing into Premiere, then splicing iun the audio and exporting from there would probably do it, but then of course you deal with extra steps and intermediate files. Depending on the length of the project that would not change the equation much, either. If you see excessive render times regardless, then this could be this ugly bug where directly rendering AE projects in AME takes hours. In such a case render a ProRes file directly from AE and convert it in a second step.

Mylenium

This is normal. AE will take whatever it needs based on your project contents, render settings and whatnot. That's a general misconception. Outside RAM previews/ caching things to RAM AE doesn't really use that much memory and those things are only relevant while actually editing. Of course the equation changes with multiframe rendering and other factors, but suffice it to say unless you use a very memory hungry effect like Keylight AE will liekly never even come close to exhausting your full RAM. That doesn't mean there couldn't be ways to boost your performance, but that would require system info and specific details about your project.

Mylenium