Network Speedtest-cli is very slow from vm trough VM to the internet

Hello
i have build a Proxmox Server. i created a virtual machine with Sophos FireWall and a 2. virtual machine with Ubuntu.

1. When i run speedtest-cli directly from the Proxmox Server i got 25/25 Gbit. So the traffic goes from the Hostsystem through the virtual Machine without any issues. The sophos virtual machine looks fast enough.
2. When i run the speedtest on the Ubuntu VM, i got only 3/3 Gbit. First i disabled FireWall checkbox, now i got 5/5 gbit/s. i am very far away from 25/25...

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