Brother, either the shop from where you are buying engine oil is not selling 100% genuine and original oil, or there is some problem with your car's engine (may be it is weak, which is highly unlikely), or oil is leaking from somewhere.
Although it is highly unlikely for 1.5L Honda City Aspire Prosmatic 2015 model, but still, do you see any blue smoke from exhaust? Or loss in engine compression? Loss in its pick, power, etc.? Or any engine oil spots on the floor, where you park your car?
I would suggest to get your vehicle thoroughly inspected from some good garage, preferably some reputed Honda 3S dealership.