Help for a school in Munich

Hello dear jitsi-community,

i am a teacher at a high school in germany and because of the current corona-situation we struggle to coordinate our internal decicion-making and to support our pupils at home. The problem is, that we lack a reliant video-conferencing tool. Therefore I tried to set up a jitsi server (Strato, 500 Mbit, Ubuntu VServer)
and it works, but the performance is very bad with several people in one jitsi-room (freezing video, very bad audio-quality, echo, …). I tried to force a lower resolution an tried to disable p2p, but it has no effect.

Nload shows (max incoming and outgoing: 20-30kbit), that it does not seem to be a bandwith-problem of the server.

Help is very much appreciated.

Thank you!