You can usually get a pretty good idea of what's going on from the physical location of the distributor. I'd set the timing at the mark on the far right and then look to see whether the distributor is dead in the middle of it's adjustment range by looking at the bolt that clamps it down and how it is positioned in the slot in the bracket. When you are set at 15* BTDC, the bolt is right in the middle of the slot if everything else is lined up as it should be (e.g., cam chains).
Make sure that the ECU is in "Set Timing Mode" before setting the timing with your timing light. And you might want to mark the position of the distributor before you move it so you can go back to where you started if you need to.