I have a 2017 model with 146K kms on the odo and the AC still performs strong without a single gas recharge till date. In your case, there seems to be an issue with the AC from factory and you need to get it checked under warranty, assuming that it is covered in the warranty.
The fuel economy of the car varies according to your driving habits and maintenance but I have never gotten below 14km/l with AC and this includes keeping the car on at idle with AC for half an hour or more in almost every trip that I make. Your poor gas mileage could also be a symptom of the AC not working properly and hence the compressor stays on for longer than it should since it's not able to cool the cabin fast enough. To verify this, run your car without the ac for a few days (if the weather allows it) and then check the fuel economy. Just to give you an idea, without AC on light foot, it is possible to achieve 18+ Km/l.
