The data transfer to or from a Samba share is very slow. Compared to a scp transfer your transfer speed through Samba is about ten times lower than the scp transfer.
Depending on you network layout you might need to set ucr variables as follows to increase your send and receive buffers:
ucr set samba/socket_options="SO_RCVBUF=32768 SO_SNDBUF=32768" /etc/init.d/samba restart
You should consider man smb.conf for further details about these options.