Is it normal for the Suzuki SX4 1.6 to show a fuel consumption of 12.4?

17 or so refers to the kilometers per liter of fuel. 😁

If you don't drive on the highway, the average is 6.6.

My original display showed 11, but after resetting it shows 15.9 [I just want to be quiet]

Abnormal, consistently below 7.

I feel something is not right.

After the oil change, the display showed 16. After a highway run, it dropped to 9.9 and is currently back up to 11.2.

Normal, both 13 and 14 are available.

It's better to recalculate it yourself, this isn't reliable.