The market expectation of prices for 15mm models is very low. A very large percentage of the price of a 15mm model goes into the cost of having it made, so the amount you clear on each sale is minimal. The trade discount is often more than I clear on a model.
Thats a pity because every time I've ordered from the states I've had to pay import taxes (which in it's self is ok, but having to pay the post office to pay the taxes isn't), so I generally just don't order from the states longer.