Car has 35k miles.

Not sure if brakes ever done, bought used at 25k as a certified car.

Sensor light came on.

Dealer is stating brakes only last 12-15k miles

Is that a for real number?

Seems lousy for a car driven very easy by the wife.

 

you should get more but it depends on your driving habit - i.e if you drive every day to LA downtown, I think 15k miles is real number

I'd check breaks manually (I think the sensor is on front passenger side) - take tire off and check breaks; if OK, replace break sensor. Before you do entire operation buy break sensor and replace it anyway if you have any doubt.

I got similar problem (when I did full right turn, it kicked my break light). MB replaced entire harness as part of warranty coverage.

 

Just turned 46k on the original pads with plenty of material left. I had the wheels off for cleaning last week, messy road tar disaster, but there was plenty left.
Maybe the previous owner was a two-footed driver?