Let's make a model in LEGO.

You can then rotate to get all three views.

Front	Side	Top

Going back to building step three, top layer has volume of $14$, so does the bottom layer.

The middle level has $4$ units.

Hence there are $28+4$ units remaining in total.

Therefore $$\frac{32}{3\times4\times5}=\frac{8}{15}$$

which is answer $D$.