SMB share is very slow
The problem is caused by Apple's home made implementation of the smb protocol.  Using smb3 won't make a difference.

Server-Side Fix

If you have control of the smb server (Samba?) then you can fix this issue by enabling the vfs_fruit module.  If you are not using Samba then you'll need to find another way to enable "Alternate Data Streams" (ADS) and intercept OSX's "special" streams: AFP_AfpInfo and AFP_Resource.  I made notes of all the details at the plazko.io blog.
On Samba server you can fix the issue by enabling vfs_fruit in smb.conf like this:

vfs objects = fruit streams_xattr


Client-Side Fix

If you do not have control of the smb server, then your only option is to change the way your OSX client is handling smb.  The only way to do that is to replace Apple's implementation of smb with Samba.  I have never done this, but there is a tutorial here.

This is an excerpt of the answer I gave to Slow SMB connection Buffalo Linkstation.