Slow Script on all pages?

Site URL: https://stamba.co/terms

Hi all, 

So we are using a template on our website. We use custom css. On some pages I added some script (for instance script to create a dropdown menu and Shopify buy buttons code blocks). In the Header Code Injection there is only google analytics and a Pixel account. However, we have a slow issue on all pages. The page provided for instance really just has text on it but is still tagged as having a slow issue with Google and GT Metrix both.

What could be the problem? I have tried removing all scripts in the header to see if that was the problem but it was the exact same results. Should we switch theme on Squarespace? If so what theme is the best with speed?

Looking forward to hear your perspectives.