Cecilia,
I have wound my bobbins by putting the thread on the pin on the bed and had fits with it. Then I ran the thread from the top pin, through the front thread guide on the face plate, down to the bobbin winder tensioner and up to the bobbin and it wound much better.
I believe the second guide is for bobbin winding. I'm not sure, but I don't think the early 15s had the pin on the bed.
Joe