When I was in Italy recently, I also had some anxiety ordering pizza, as looking around, everyone including Italian kids had an entire pizza each. The pizza was not small, it was easily 11-12 inches wide.
In the end I ordered only 1 pizza for 2 to share, but I also ordered a few starters and drinks. So I guess its about the same cost as ordering 2 pizzas. Anyway didn't get suan like these tourists. LOL
And in the end, I noticed a lot of the Italian kids didn't finish their pizza, they had leftovers and they didn't ask for doggie bags