We’re introducing a group of people in East Africa to our discourse as part of a learning exchange, and I have to say discourse has been holding up well! Even on slow 2g connections I am able to keep up on discourse and manage topics and users etc. I’m even doing an upgrade right now. 
One area where we seem to have trouble, however, is with uploading pictures. Some participants have been trying to upload one or more pictures at a time and the composer then takes a long time to upload the files. Often no more than one or none of the pictures are uploaded successfully and the word “Uploading…” remains in the saved topic instead of the picture.
I’m not sure there’s any easy solution to this and I know we are not the main clientele for discourse. But, at the least, it seems to me the error handling should be more robust. Instead of failing silently it should display an error with some advice on what to do in slow internet connection situations.
Another alternative that would be nice would be the ability on the upload interface to resize the file to be uploaded locally on the device before uploading.
Our biggest competition here is WhatsApp - everyone is on it and even uses it to set up ad hoc groups to coordinate activities. They understand the benefit of discourse for engaging with a larger network but are using WhatsApp for logistics and sharing pictures with each other instead of discourse because it “just works” while discourse is error prone on slow connections.
Update: everyone in our group uses android phones, btw, and I am talking here about tribulations with uploading pictures using android.