There are two important parts to a stop-limit order. The stop is the trigger price and the limit is like your regular buy/sell price. It means you're willing to buy/sell at the stop price, but not beyond the limit price (no more than the limit when buying, no less than the limit when selling). When selling, a market order to sell at the limit price will be placed when the highest bid drops to or below the stop. However, if you put in a buy stop-limit, then when the lowest ask price goes up to at least the stop, a market order to buy will be place at the limit price. So in your example, the price ($10) was below the stop ($15) which would immediately trigger a sell order at your limit price, but won't trigger a buy until the price hits $15.
Check out video:
