I had the same problems! I've got linux on my computer, used GIMP to shrink the file, and used the "advanced settings" in the save file dialog. I unchecked the "save exif data" and, more importantly, "save miniature" I don't know how it is called in the english version, maybe save thumbnail. You're ditching the little preview picture you see in your file explorer when you look at all your pictures. It's not necessary when you have a small picture, it's like saving you picture twice, doubling the size of your avatar. My avatar is now 9,4KB