Personally i wouldn’t be overly concerned with that opportunity in Desktop as the savings proposed are not that great.
To fix it would require either:
1. better compression of your original images – which would require re-uploading new images.
2. Use a plugin/3rd party image compression app – which comes at a cost.
3. Register a new Image Size for the WP Media Attachments thats is a better fit for your needs eg. a 720px wide image, then regenerate all thumbnails and select your new image size in the customizer. This of course will add more files to your database.