Elixir requests slow in docker with phoenix code reloader on
There are two things: the code reloader, which compiles your code on every request and the live reloader which scans your filesystem for changes. The code reloader should be as fast as calling mix compile. The live reloader is fully optional (it is just to reload via websockets).
If the issue is in the live reloader, you can either remove it or you can restrict the directories it watches for performance. See the relevant note in the README: https://github.com/phoenixframework/phoenix_live_reload#backends