If you were to send a bottle rocket 15 kilometers up into the air which layer if the atmosphere would it be?

If you were to send a bottle rocket 15 kilometers into the air, it would reach the lower part of the stratosphere. The stratosphere extends from about 10 to 50 kilometers above the Earth's surface, with the tropopause, the boundary between the troposphere and stratosphere, located around 10-15 kilometers depending on the location and weather conditions. At 15 kilometers, the rocket would be well above the troposphere, where most weather phenomena occur.