Your driving something the volume and mass of the Death Star and this was unexpected
15mpg was a little shock if I'm honest but no you are right I can't expect mid 20's from that kind of engine and an auto box with more gadgets than bond.
I do feel a little like a baby seal must somewhere die every time I start the engine though
Base price just over 42k then you have to add options on - leather, dynamic seats, sat nav, double panoramic roof, memory seats, wood steering wheel, airmatic suspension, AMG alloys, 6 cd auto changer, parktronic.
I hesitate to even try and guess with all that but each of those options was crazy expensive - got to be cracking on for well over 50k I guess.