SMB performs very badly on high latency links. 

SMB is designed to use over LAN and it is chatty protocol. When SMB is used over WAN even with WAN optimization, user experience might be still not good.

Follow below steps to get better performance while using SMB:

• Always send SMB traffic via low latency link. Use Versa Traffic steering capabilities to to use low latency and low packet loss path.
• Enable TCP optimization. Configure TCP proxy on both VOS device in SMB client location and VOS device in SMB server location. Use congestion control as BBR, loss detection RACK.
• Follow performance tuning guide links from Microsoft - https://docs.microsoft.com/en-us/windows-server/administration/performance-tuning/role/file-server/smb-file-server
• Follow this instruction from Microsoft - https://docs.microsoft.com/en-us/windows-server/storage/file-server/troubleshoot/slow-file-transfer