Yes it can give 17+ but then the speed should not exceed 110 km/hr in any case.
My 2009 Gli gave 17+ average on our last trip from Lahore -> Topi (GIK) -> Islambad -> Lahore.
Total distance traveled = 1000 km approx
Total Petrol Consumed = 57 liters
Speed on M2 and M1 = 100 km/hr avg (110 km/hr max) with AC on step1/2