Modal loading entire site

Hi
I am using the link <a href="4915" class="modal-link">Open in Modal</a>, but the modal window is loading the whole site – headers, footers and all the scripts. I thought it was only supposed to show the content? I assume this is why it is slow to load?
Also, there’s no loading spinner.
Thanks for your help.
Ian

The page I need help with: [log in to see the link]