you have a 100mb LAN. That is 12.5MB/s. Or 750MB/min.
That is theoretical. Scale it up to 45GB/hour.
You are actually getting 16GB/hr. That is way down in the LTO-1 range. The speed problems are generally caused by SCSI chain / SCSI driver or termination issues. What else is on the chain, what level is it and active or passive termination? Up to date drivers? Try windowsupdate and look for driver updates. If there is an enabled BIOS, check it is properly configured.