It looks like you don't have caching on that site.
In the WebUI go: Security > Nginx config
Uncomment this section, editing the 600s section.
proxy_cache_valid any 600s;
add_header X-Cache-Status $upstream_cache_status;
proxy_cache my_cache_fledd.it;
proxy_ignore_headers Cache-Control;
proxy_cache_methods GET HEAD;
proxy_cache_bypass $cookie_nocache $arg_nocache;
proxy_cache_use_stale error timeout updating http_500 http_502 http_503 http_504;
Press the Update & Restart Nginx button. Pages should then load in ~2sec rather than ~4sec