1. A unit of measure meaning 15,000 of an item. It is most commonly used as an exaggeration of something. It is 10,000 times a bitch or 1,000 times a bitchful. With no noun after, one can assume it is being described in weight, depending on the region where you are it could be pounds or kilograms.
2. It could also be used to describe an area where people live, normally the nicer regions of a city or town.
I have a bitchton of coffee cups at my house.
That truck must weight at least 2 bitchtons.
That guy lives in the bitchtons of manhatten.