Do you have Autozone stores in your area?
If you do, they sell Mobil1 OW40, I use it here in the mid atlantic where summer temps are quite high.

That OW40 when the temps are high is acting like a 40 weight oil.

If I were driving at constant speeds above 100mph a lot, and soon afterwards sitting in heavy traffic jams, then in my opinion that may make me think about Mobil1 15W50.

But, for normal sub 80mph drives and urban traffic, and your horsepower figures for your car aren't really pushing any limits, 0W40 or 15W50, either

get the Mercedes booklet !!