You should read some guideline on centos, please RTFM, nethserver is no more than a centos.
You should come again with the load and what services is running on your server and the bandwidth when you try to login, (open a terminal an gather the information)
Thanks for pointing to the right link to make your suggestion inclusive like we are used to in our community⊠Maybe you can even opt to remove the rtfm part in your previous post.