Turning on Low Quality Image Mode in iMessage can help you use less data, preserve battery life, and can send images more easily when your connection is not so great. With it enabled the images sent will be notably lower quality, but when data and battery is a significant concern, it can be a great option.
To enable Low Quality Image Mode
Open “Settings” and go to “Messages”
Scroll all the way down to the bottom of the Messages Settings and toggle on the switch for “Low Quality Image Mode”