UPDATE: There are two issues here. The answer to the question regarding LPR/LPD is resolved here while the other issue was relating to the actual print stream is answered at the bottom of this response.
Ensure your firewall is off (or at least allowing 515 to pass through). Also, ensure you are using the IP of your network adapter and not local host as LPD tends to bind to an actual IP address.
If you want to ensure that your data is passed through without modification / encoding then use -o l in the command line. For example:
lpr -S <workstation_ip> -P <printer_share> -o l test.ps
lpr -S 192.168.1.6 -P P510L -o l test.ps
Also ensure the file you are sending is actually supported by the print device. While some printers support graphic formats most are expecting PCL, PS, XPS, PDF etc. Some support TIF and other JPG etc. Ensure the file you are sending is supported by the device.
In the end the issue appears to be the proprietary nature of the device and as such, the requirement is there to push the file through the print driver. One simple way is to use a graphics application that supports command line printing. One option is MS Paint.
mspaint /pt IMG_1234.jpg "Hiti P510L"
The printer name (Hiti P510L) is the name that appears in the devices and printers screen in Windows.