It’s possible to set up a cache for incremental builds, but it’s not super straightforward: CCache - NixOS Wiki
There are some other techniques, like building the cache as a separate derivation in nix, there was a ‘nix hour’ about it: https://www.youtube.com/watch?v=1tEur9Tzv9c
It was also recently discussed: Nix *could* be a great build system
So doing it in the shell with nix-shell is still the easiest, you can actually run the build as defined in nix but manually by calling functions: The Standard Environment | nixpkgs