Jekyll serve to cache elements

I have a big project with data files, loads of includes and sass, but my project takes 12-15 seconds to reload is there a way to only get jekyll to cache pages your not working on etc.

Have you tried using incremental builds?

Incremental build

Enable the experimental incremental build feature. Incremental build only re-builds posts and pages that have changed, resulting in significant performance improvements for large sites, but may also break site generation in certain cases.

jekyll build --incremental

Is this instead of Jekyll serve while working on it

No not exactly. You can use the --incremental flag with jekyll serve too. Or you can enable it for both build and serve by adding incremental: true to your _config.yml file.

You may experience strange things using it though. Because of the way it caches files things don’t always behave how you’d expect. If you have a fairly simple site you’ll probably be OK.