You should be able to leverage generate_for in your build.yaml with include/exclude to reduce those build times significantly. You should be able to get it back down to a few seconds including building the graph and then you should be able to just run watch instead of build.
It may be worth mentioning that build_runner's graph contains every single asset that might be generated. So when selecting what's included and excluded you can reduce the graph size dramatically.
It may be worth mentioning that build_runner's graph contains every single asset that might be generated. So when selecting what's included and excluded you can reduce the graph size dramatically.