Part 1: https://forums.meteor.com/t/how-i-made-our-app-35-faster-in-build-rebuild-browser-load-time-size
Part 2: Docker. Caching assets (~/.meteor, node_modules) and tmpfs's (ramdisks). Namely RAM disks for:
~/.meteorapp/node_modulesapp/.meteor/local/isopacksapp/.meteor/local/plugin-cacheapp/.meteor/local/bundler-cacheapp/.meteor/local/buildapp/.meteor/local/shell
How do you work? Easily, use Docker bind mount to allows you to write code from your OS, but expose the app to Docker from the Host machine.
Happy hacking.