How long do you think it will a defrosted stone baked shop pizza to cook at 150 degrees celsius?

Long enough for the cheese to bubble and brown, before allowing anything to burn. Any guess in minutes will be wrong, because there's too many factors that can affect baking time, such as the thickness of the crust, sauce and toppings, and the kind of toppings, since some burn more quickly than others. Your oven makes a big difference too. For a better crisping of the crust, preheat a pizza stone or cast iron pizza pan and use a pizza peel or flat cookie sheet to quickly put the pizza on the hot surface, so that you don't lose a lot of heat while the oven is open. It's better to preheat the oven hotter, like 200 deg. C, and then reduce to 150 for baking. This lets the oven temp recover more quickly for nice browning.