Sounds like this is the primary cause of any issues your Mobile Technicians are having. If you don’t have a good connection, it doesn’t matter what you do.
Don’t see how using email to update tickets (you should be able to) would be any different as you are still needing to upload the same image.
Reducing the Res may be the only solution. Especially since some cameras can take 200 megapixel images. Just for reference, 1080p is only 2 megapixels.