I’ll inquire with Discourse to see if there’s anything I can do about performance issues for lower-end hardware. The custom CSS or images on this site could probably be cleaned up or optimized, but I’m not sure it’ll completely solve the issue you’re having.
I’ve personally never run into autosaving causing issues with typing out a message, but it’s something I can bring up to our provider. What’s the model of phone you’re using and what are its specs?