Whats the highest millage for a dodge avenger 2012 Is it a good car as far as transmission and engine Thinking about buying one?

No to used Chryslers.

There are good miles and there are bad miles. One could find a 175,000 mile car that is in far better shape than a 90,000 mile car.

Lets say that the 175,000 mile car is a single owner car and was driven on the highways between Phoenix and Tucson as a commuter car and was meticulously maintained. The dry climate prevented any rust and because it was driven mostly on smooth highways, the suspension is in fine shape and the body is free from dents and dings.

The 90,000 car was driven around Detroit as a daily driver by a careless bachelor then sold to a College student then sold to a pizza delivery guy. It spent its life as a "beater car". It received little maintenance and has rust all over it due to the harsh Detroit winters.

The moral of the story is that you cannot judge by mileage alone.

I believe the current yearly milage is 15,000 /year.

It's 8 going on 9 years old. It should have 100 k or less