• Use zram so swapping doesn't immediately slow things to a crawl.
• Use cargo check, often. You don't need to always compile.
• Add a release-dev profile that inherits release, use cranelift for codegen in it, and turn off lto.

Otherwise, it would be useful to know what kind of system you're running, and how is the system load without any rust dev involvement. It would also be helpful to provide specifics. Your descriptions are very generic and could be entirely constructed from rust memes.