You may need to clear cache and cookies to see the new images on the live website. Try hitting CTRL-F5 on your keyboard when on the page that you have published the new images. If that doesn't work you can usually find a "clear private data" or "delete browsing history" under "tools" in your browser.
The slow loading may be caused by the images being large file sizes. The only real work around if that is the case is to have smaller images or images with smaller file sizes. That usually results in less clear images though, so that may not be something you wish to do.
