As you travel from 15 degrees S latitude to 15 degrees N latitude, the primary change in air currents would be related to the convection pattern (A) and the general circulation of the atmosphere.
At the equator, warm air rises, leading to convection currents. The Coriolis effect would also influence the wind directions as you move northward. While you could observe changes in jet streams (B), they are generally located at higher latitudes than 15 degrees. Air current directions (C) and wind directions (D) would also change as you move along this latitude line, but they are part of the larger convection pattern.
Thus, the best answer in the context of air currents would be A. convection pattern.