routeros vmware tunnel problem

Hello
We are running Routeros on four supermicro servers.



we have tunnel on two servers to each other.
one of the server is pppoe server with 1500 users.

they are in different places.

tunnels are bridged to pysical interface.

Problem:
when we run bandwidth test from one servers physical interface ip address to another. test can pass 700 mbps.
but when we run it on eoip tunnel it can pass max 300 mbps when pppoe server have about 200-400 pppoe clients, but if pppoe clients are more then 500 it can pass less then 100 mbps tcp traffic.


we cannot find solution.
Can it be mtu problem?
Thank you