can I minmize HTML5 file size exported by unity to less than 10MB

I want to export a very simple 3D project to WebGl, it gives me s size of 30MB, can I minimize the size to less than 10MB.

Yes, quite easily if you have a mod_rewrite enabled server you’re uploading to.
First make sure stripping is on in Player Settings and optimisation level is set to Fastest (very slow builds) in Build Settings.

The “Compressed” should be less than 10MB now. You can delete the “Release” folder, and then just upload all the remaining files including the .htaccess.