Why does it still take so long to initialize in mobile compared to desktop? How can it be improved?

In Android, once the script is loaded, it takes 3.5 seconds to process it.
Screenshot of Network Activity panel: https://i.imgur.com/aW6HmZS.png

So I end up getting 8-10 seconds initial loading (cold) and 5-6 seconds in hot.
If I switch to other apps and come back, if the app is killed (happens often), I need to wait those 5-6s again, which makes it quite impractical for a mobile app.

How are you guys dealing with this?

(Not using Cordova)