Poor Network Performance on Hyper-V in Windows Server 2020 using dell poweredge r740xd

Hello,

I have two dell poweredge r740xd servers which are linked with 25g SPF cables to a dell switch in teaming mode for each, and they are in trunk mode VLAN. I try to test the bandwidth using iperf but when I run on the cmd of the first server, the iperf command  (iperf3.exe -p 5201 -s) and on the other, the client command (iperf3.exe -c X.X.X.X -p 5201 -i 1 -t 0 -p 5201 - i 1 -t 0 -f g) 
I see that the throughput is 7 Gbits/sec and when I reverse the roles of the two servers, I see that the throughput is 9 or 10 Gbits/sec.
I've tried disabling some features at the server NIC level to see if the throughput optimization issue comes from them, but no, I haven't figured out where the problem is yet, in normal I should have minimum have 15 Gigabits/sec