I use amethyst this way on mobile but it still ate most of my traffic. I don't believe that jpgs are the reason why nostr is so data-heavy.
2 Things you can do yourself: - You have 11 read relays. Lower it to 3-5 - Use clients with outbox model And some things are too late to change. Kind 1 and e tags are overloaded. This means that clients will always receive data they don't need. Unless the client wants to show root posts + replies and fetch the whole thread instead of just the next level of replies.