That looks like a very complex sheet, especially with the way the sheet workers are written. I can't try to diagnose that, it would be way too time consuming.
To find out if the problem is in the sheet workers, put return; at the start of each sheet worker and see if the problem goes away. (Much of the sheet's functionality will stop working, but it'll help you narrow down where the problem is, if indeed it's in the sheet workers).
Or for that matter - just remove everything between the two script lines (make a copy), and see how the sheet's load. If it's now super fast, you know there's something in the sheet workers that is causing an issue, If not, the problem is somewhere in the HTML.