If you are able to successfully send that by resizing or re-encoding, you should be aware that the image will be resized so that the smallest dimension is no larger than 768px. That means you are basically sending something that will be interpreted at 768x768, and in four detail tiles.
Here’s a snippet for constraining the size and cost, by a maximum dimension of 1024 (where the maximum dimension on a long skinny image like in the first post is normally resized down to 2048).