Is this normal?

[JC]

With trips consisting of 15kms only, it would take about 7kms for engine to heat up properly - all the while it is in rich mode, so uses more fuel. If it's stop/start driving, then yes you will chew more also.

In my AU XR8, I used to get around 420 average per 60 odd litres on petrol. MY AU I6 wagon gets between 420 and 500 on petrol, but that is a mix of city/highway, with some trips no more than 8 km each way, but others around 25 to 30 each way, on freeways/highways.

You should see anywhere between 13 and 16 l/100km on city cycle and still be "normal" - so for 400 km, you could expect to use anywhere between 52 litres and 64 litres. That's 12 litres difference, or $14 odd per tank. My advice - put the car in power mode, and drive it in 3 unless you go over 80, in which case shift up to D - just make sure you go back to 3 when going less than 80. Try it for a tank and see - I'm betting you will get better results.