Hello,
The fact is, there is no cache in our demo website.
No Joomla cache, no cache plugin, no optimization plugin.
We are simply using a Linux server but instead of having a classical apache web server, we are using nginx and php-fpm.
FPM provide some PHP file pre-process cache to speed up the loading of PHP files.
And afterwards, with a lot of memory in the server, the servers (nginx, mysql, fpm, etc) can use the linux disk cache feature to make the file accesses faster.
Afterwards, we could still see to activate some cache/optimization plugins in Joomla to increase the speed but since it's a demo website which is refreshed every 4 hours, the interest is limited.
I can see that your website is hosted on a Windows+IIS server. You should see to first perform some optimization in that side before trying to add plugins or else in your Joomla.
Regards,