I bought a new cadillac cts 2014 (v6) 6 Months back, but I have noticed that the Oil Life is dropping faster than what I was expecting, knowing that I do get a free service every 15,000 KM, is it normal for oil life to go as little as 20% for a car that has done only less than 5,000 KM ??... Any reason for this happen in normal situations ??..