P0015 code can be about replacing a broken oxygen sensor can eventually lead to a busted catalytic
convertor which can cost upwards of $2,000. Taking your car into a shop will
cost you around $200 depending on the car. However, an oxygen sensor is easy
to replace on many cars and is usually detailed in the owner's manual.
If you know where the sensor is, you only have to unclip the old sensor and replace it with a new one.
Regardless of how you approach it, you should get this fixed right away.