Who can tell me why PDF files exported from CAD / revit are slow

In Illustrator, I work with PDFs that were exported from CAD/Revit architectural programs and they are painfully slow. Is there a way to connect with someone with Adobe or a third party who can examine a sample file and tell me WHY these are so bad?

I've tried all my tricks and researched, but I don't know what else to try. If someone could specifically say what's going on, I could try to fix it in my files. Or I could tell the architects what to do differently.