Yeah, large image files are one of the biggest reasons pages slow down or break while loading 99% of the time. Now, there's always going to be some loading time if you open any page for the first time or restart your cache and reload the page... but there's always room for improvement!
I recommend checking out
TinyPNG for reducing the size of your imagery and
Dither Me This if you wish for more stylistic results. I would also suggest utilising more .jpgs (or even .gifs) than .pngs (unless you want transparency of course).
For instance, since my site is image-based and hence image-heavy, I try my best to keep the majority of my images below 1MG (which also helps me with storage management). High-quality images are not recommended, especially if they are plainly decorative or used in impact spots. A super tiny and pixel-ish image can look as decent as a heavy one from afar!
Also, another reason why pages may take a while to load are due to external attachments. Often such files are already compressed within the external site, but that doesn't necessarily change anything. I reckon the page trying to capture data from multiple instances at once is causing further delays. So, I would recommend you host your own files within your site and modify them to your own liking. Well, unless you are using some short of widget code snippet that cannot be altered easily.