Make npm run watch only compile specific assets

In my webpack.mix.js I have 2 separate Sass and JS bundles as stated below:

//Public
mix.js('resources/js/app.js', 'public/js')
    .sass('resources/sass/app.scss', 'public/css');

//Admin
mix.js('resources/js/admin_app.js', 'public/admin/js')
.sass('resources/sass/admin/app.scss', 'public/admin/css');

The second "admin" bundle rarely changes and does not need to be compiled.

How am I able to get npm run watch to only compile the "public" bundle. The admin bundle adds a significant amount of time so if I could only have the "public" bundle compile even if that means I could use a command like npm run watch --public, that would be ideal.

Any ideas? Thanks