Virtualmin needs HTTP/2 support. Virtualmin doesn't provide support for Apache mod_http2 on CentOS 7. Attempting to add support via third party repositories doesn't work either since Apache usually isn't compiled to serve content from /home.
I realized first hand the performance differences between HTTP/2 and HTTP when using TinyTiny RSS on a virtualmin server vs a cpanel server that supports HTTP/2. The performance boost is considerable.
You can see the performance differences yourself by going here: HTTP/2 Demo