15.
Rotate the model by 45 degrees in the clockwise direction.
Prepare to apply a valley-fold.
As you can see from the picture, the valley-folded line should be located at a little more than half (= 0.586) as measeured from the outer edge.
16.
Apply the valley-fold of the step #15.
Prepare to rotate the model by 90 degrees in the clockwise direction.