Minimum requirements for the server hardaware

Gentlemen, what would be the minimum hardware requirements for the server control 15 players?

Depends on your ‘interactivity’ needs and how complex your displays are going to be and be modified. I’d suggest a small VPS would do for just 15 players. Something like a NUC with an SSD should be more than enough.

I ran 14+ clients form a old Dell Opti 745 for 700+ days without major failure and 234 days since the last
boot before that ( native install ). Now I have started running my current server build as a Virtualbox VM
on a R900 which is my old testing VM host. I run normally 2 cores / 4GB ram with dynamic disk with not
to many issues. If you get weird Virtualbox VM freezes, make a snapshot and update the hosts VM
package. Seems to fix most issues.