Go to the Samsung's website and get the PPD for ML-2150. This should install inside /Library/Printers/PPDs/Contents/Resources/en.lproj/.
Open the file "/Library/Printers/PPDs/Contents/Resources/en.lproj/Samsung ML-2150 Series" using a text editor.
Find the line "*OpenUI *Duplex/Double-sided Printing: PickOne"
Insert above this line the three lines below:
*%========================================
*% Duplex Mode
*%========================================
For some reason OS10.2 does not require these three lines.
save the file.
Set up the printer with "Printer setup utility".