TTFB is extremely high. You need to first reduce that before working on other changes.
Basically, you’ll need to identify the place where the generation of the page is being so slow - is it at the app server / database server level? Or is it at the connection to your data center.
To me, it looks like an issue with the app server / db layer issue. You could take a look by trying to answer these questions:
Is this being dynamically created? If so, can you enable database caching?
Can the final HTML itself be cached on the web server?
After you fix these things, you could consider using a Content Deliver Network (CDN) to cache the pages closer to end user and reduce the latency. This will bring down the TTFB further. You could then continue to investigate and fix the other page load issues.