For example an US Gallon of petrol is about 6.6USD right now
Petrol in the US is very cheap compared to other western nations, so it is not a very good indications of prices. You are better off looking at the The Big Mac Index to do comparisons.
So how in the word is it possible that in the US 15/hour is barely a living wage? How wasteful a life are you living there seriously?
In a word .. extremely. With 2400 sq foot homes being normal, and 3000 sq foot home not unusual, and the car being the basis of personal transport what do you expect?