Discourse lazy loads large images that are outside of the user’s view to avoid the issue of loading many images at once, a little detail here: Lazy Loading Images
Discourse also adds and removes posts from the document as you scroll through a topic. This allows the application to maintain performance in situations where there are hundreds or thousands of posts.
Maybe 1500 images could work… though this is incredibly variable along with image size. There’s a big difference between a 15kb and 5mb image.
If you’re worried about performance and can’t be bothered to test it ahead of time… I’d second the recommendation of splitting the images across multiple posts so you’re utilizing our auto pagination feature alongside image lazy loading.
Do not count on this happening based on a single person’s request, especially not for free within that amount of time. To be completely honest it’s a bit silly to even suggest it.