Thanks for pointing that out. By coincidence, I was checking this now as I was actually worried about the bandwidth bill from my cloud provider and I wasn't aware that Nginx doesn't compress everything by default.

Simple tweaks:

gzip_types text/plain application/xml application/octet-stream application/javascript audio/ogg;

wasm-opt -Oz out/bevy-shoot-em-up_bg.wasm -o out/bevy-shoot-em-up_bg.wasm

So now , the total download size is 6.4 MB.