One of the main reasons why your website may run slowly is poor configuration. WordPress is the most common CMS for building PBN sites, and it's also the easiest one to mess up.
It's common for WordPress users to set up a large number of heavy plugins, which then slow down the site. Please remember that WordPress will process every single plugin you have as soon as the visitor hits your site. If you wish to have a fast website, use as a small number of plugins as possible. Also, delete all deactivated plugins and themes.
If you wish to use a caching plugin to make your website load faster, then we usually don't recommend that. We are already using a caching method that serves your PHP files from memory, and using a caching plugin may just make your website run slower because to server an additional static HTML cached file, the PHP script needs to do additional work, which then uses additional IO. You really can't make WordPress faster by adding more plugins to it. If you have a special reason why you need to use a caching plugin, use it, but if you don't, we don't recommend using one.
We have set up specific limits for every single network (cPanel account). They are there to protect our servers from abuse and rouge scripts that can take down the whole server. When your websites start loading slowly, you may wish to look at your account's resource usage. You can do that by going to cPanel and then clicking on the "Resource Usage" link under the "Metrics" section. Then click on "Current Usage" to see how your account uses resources allocated to it. Most commonly, you may see IO or Memory usage reach its limits. If that's the case, contact us, and we can increase your account's resource limit for you.
That's actually not a hosting issue, but more a problem with your website itself. Sometimes it can happen, especially if you use external Javascript (for analytics or tracking), that your website is stuck on a white page for a long time and then suddenly loads. This happens when the Javascript file is loaded between <head> tags, and the external source is not responding fast enough to the request. This issue will cause your browser to be blocked from rendering the rest of the website. So, if possible, make sure your external Javascript/CSS files are loading as fast as possible at all times or put external Javascript before the </body> tag of your website (you may also use async attribute).
