Miserable performance of Hyper-V storage on CSV
If you use Broadcom NICs, try to disable VMQ on a virtual switches and on a physical network adapters: http://www.dell.com/support/article/ua/ru/uabsdt1/SLN132131/EN
You might also check if there are the latest hyper-v drives installed.
Besides, are your VHDX files formatted to NTFS?
One more thing that comes to mind is MTU. Try to change it to 9000. But usually it gives just a little increase of performance.