$\text{cost per square inch} = \dfrac{\text{Price}}{\text{Area}}$
Large pizza:
$\text{cost per square inch} = \dfrac{15}{\frac{1}{4}\pi (16^2)}$
$\text{cost per square inch} = \$0.075/\text{in.}^2$
Medium pizza:
$\text{cost per square inch} = \dfrac{7.50}{\frac{1}{4}\pi (8^2)}$
$\text{cost per square inch} = \$0.149/\text{in.}^2$
The better buy is the large pizza at \$0.075/in.2 only ← answer
