Latency VPS ubuntu 20.04 with graphic interface

Hello,

Here I am on this forum because I have to create 30 instances for a training course and its people would need to have an ubuntu instance.

The instances we took are D2 instances which match the following specs 4GB RAM, 2vCores, 50GB NVMe storage, and 250Mbps.

We then installed a graphical interface on the different instances.
We connect in RDP via the public IP and when we connect it works fine however we have at least 3 seconds of latency between window moves.

When we are on the terminal inside the VM it also works without latency.

Today we have tried to change the RDP access, to put a lighter graphical interface, to virify the bandwidth at the server level and always the same.

Secondly, we looked at the resources monitor to see if the machine supported the graphical interface and we are at 30% maximum of use of all the capacity of the VM.
We are currently stuck with latencies.

Thank you in advance for your help.