configure multiple sshd instances on debian 8 (jessie) systemd

The default Debian 8 systemd sshd unit is in /lib/systemd/system/ssh.service and is pretty simple. All you would need to do is something like cp /lib/systemd/system/ssh.service /etc/systemd/system/ssh_sftp.service then edit your file to be something like this.

[Unit]
Description=OpenBSD Secure Shell server
After=network.target auditd.service
ConditionPathExists=!/etc/ssh/sshd_not_to_be_run

[Service]
EnvironmentFile=-/etc/default/ssh
ExecStart=/usr/sbin/sshd -D -f /etc/ssh/sshd_sftp_config $SSHD_OPTS
ExecReload=/bin/kill -HUP $MAINPID
KillMode=process
Restart=on-failure

[Install]
WantedBy=multi-user.target
Alias=ssh_sftp_d.service

After creating that file, enable and start it. systemctl enable ssh_sftp.service and systemctl start ssh_sftp.service.

Like @Michael Hampton suggested, basically the exact same set of instructions as what was suggested for the Redhat.