does it cost $1,500 to replace a catylitic converter on this car

Shop around. The code stored in the computer of your car is likely a P0420 it signifies low catalytic converter efficiency. Here in California we have to fit CARB approved cats which are very expensive a muffler shop may be able to fit a universal cat to your Sienna.

You may be able to find a better deal, but the usual cost IS around that price. You will be able to find some lower and higher. Your best bet is to ask around and get prices. You should expect anything from $1,000-$1,700