How are you setting the tool height?
Have you tried to manually jog to that 15.6 mm depth? Is it possible that the tool is shorter than the other ones and you reach the end of Z axis travel?

You can scroll the g-code to the end part where it cuts at full depth to see if it has the Z-15.6 or Z0 or Z-0.6 command, depending on where you have set the the Z0, on top surface of your workpiece or on the surface of the table..