KirkClemons's post in Large Empty Layout was marked as the answer
How do you typically create new layouts and update your template?
There seems to be a lot of older data from X6 and maybe older in this file. There are even references to objects that would normally be in a plan file, not a layout file. This is probably what's adding to your file size.
I would recommend copying your title block into a new layout and saving the new layout file as a template.