Issue Slow new websites in loading

[myfender]

Hello everyone,
I have a problem when I create new websites, they go very slow. This happened when I updated to version 17.8.
As an example I did a test with an existing site by copying it in the same subscription with a new domain.
The old site is VetrineItalia :: Centro Commerciale Online (and this is pretty good)
The copy site is VetrineSarde :: Centro Commerciale Online (this takes a lot of time, as if uploading the images one by one).
I can not get over it, it's not the php (I tried the 5.6, the 7.0, 7.1 and 7.2) and it does not seem mySql ...
The settings are IDENTICAL, they are in the same subscription.
I noticed the problem when I activated a new website (Scontatissimi) and from there I deduced that every activation was slow.
This is instead a site that exists since before the update and has no problems: Dimensione3D.com.
Obviously I tried the various "plesk repair" without success and I checked from "Webserver Configurations Troubleshooter" that there were no damaged files.
What can I do?
Thank you

 

[Brujo]

As starting point check: Troubleshooting slow websites & Slow website performance: Load Average value is higher than CPU cores count

take also into consider to test your websites with some wellknown tools like:
GTmetrix | Website Speed and Performance Optimization
Pingdom Tools
Web Server Security Test | High-Tech Bridge

to get information about the difference of your websites, it seems there is a lot of room for improvement for your sites and it will give you some ideas about optimizing the content of your site, at least..

Also you can think about to use nginx as proxy cache for your sites
How to enable Nginx reverse proxy in Plesk
HTTP/2 Test | A simple HTTP/2.0 test tool - see: Does using HTTP/2 improve site performance?
HTTP/2 Support in Plesk