Toyota corolla 1.4d esteem rear breaks poor quality

I've recently taken my car (2019 Toyota corolla 1.4d Esteem) for a service at Barloworld Toyota Kuils River for it's first service (15000km). The service itself was a breeze and was done professionally. However what amazed me is that, I was told that my rear brakes are at 45% (which is a cause for concern) and the front ones at 85% (which is a fair indication of the kilometers driven). My issue is, how can a brand new vehicle go through brakes so quickly in such a short span of time. I hardly carry passengers at the back, let alone luggage. I'd have expected that the front brakes wear quicker than the rear since the car is front wheel driven. Surely something like this should be considered for warranty cover? I'm really not pleased at all