Customer uploading large filesize images

Good evening all,

I have a customer using the responsive realtorpress theme. They love the functionality of the theme. I am concerned though regarding their image uploads, their property pages are taking ages to load because they keep uploading images around 5mb. I have reduced the size of the wordpress media settings to 600 x 600px instead of the original 1200 x 1200px. However the file sizes are still huge. Can anyone recommend a solution or a good resizing plugin, I am currently using Ewww Image optimizer which does improve filesizes but ideally I want to get these down to 1mb otherwise they are going to fill up the server storage really quickly at average of 5 images per property at 5mb. I can’t seem to convince them to reduce them prior to uploading them.

Thanks for any help.