What are the x-intercepts of a parabola with a vertex of (-1,-16) and a y-intercept of (0,-15)?

The vertex-form equation is
  y = a(x+1)² -16
Putting in the y-intercept values, we have
  -15 = a(0+1)² -16
  1 = a . . . . . . . . . . . add 16

Then the x-intercepts can be found where y=0.
  0 = (x+1)² -16
  16 = (x+1)²
  ±4 = x+1
  x = -1 ± 4 = {-5, 3}

The right answer is option d.