It takes longer to cook a large cheese pizza than it does to cook a small cheese pizza because of the thermal heat it needs to conduct through the pizza. A small pizza contains only 150 grams in mass, meaning it should take less time to cook a pizza with less size and mass because of all the heat conducted through it. On the other hand, a pizza greater in mass should take more time, due to its conductivity in thermal heat to cook it up. So this means if you heat it up in an oven, it will take more time and heat to cook it up, unlike the small pizza.