Have had this car few months now got it brand new and I’m averaging around 15 mpg. I live in Chicago most of my driving is on the streets no highway. Is this normal. When I do take long trips on the highway I can average about 28mpg. Also with oil changes they told me every 6-7k at dealer I currently have 6600 miles and have changed it twice already. Got it changed at 5% is this normal?