I don't know what you mean by your "upper level", but you have 15 amps at 240 volts available. For a continuous load, which is defined as 3+ hours of "on" time, you are limited to 80% of the breaker rating, which in this case would be 12 amps or 2880 watts. Non-continuous loads can use up to the full rating of the breaker. A "double-pole" breaker refers to a breaker that protects two hot legs simultaneously - a 120 volt circuit only has one hot wire, so it uses a "single-pole" breaker.