150,000 miles. Reasonable to need a new cat converter?

Hello, It isn't unusual at all, however it may be able to be cleaned. We have had success with cleaning them and extending the life for another couple years. You have some options, have you had a technician test and diagnose this for you? If not it would be worthwhile to do so. Hope this helps. T

You're putting the cart before the horse. Get the code pulled at fix it.