admin/config page taking around 30 seconds to load; the rest of the website loads fast
The admin/config page can trigger a check of the site 'status report' which depending on the modules &amp; services your site uses may check for the ability to connect to certain services. 30 seconds sounds like it is trying to use some service but throws a timeout after 30 seconds. Try checking the status report under working / not-working conditions to see if some services are being blocked.