My html build size is about 9mb
The default engine is ~5mb for HTML5. Do you count the content in your 9mb?
You could also try to remove the physics engines if you currently don’t use them?
Try the helper app to create your manifest file: Manifestation - Create App Manifest files with ease
Also, for textures on HTML5 you might want to look into WebP compression and texture profiles
That should help a lot too.