Instructor pilot reported loss of engine power on descent and continued to landing at the destination airport.

Narrative

My student began a descent from 6;500 feet MSL to ZZZ. Passing through 3;000 feet MSL; mixtures were placed full forward and fuel pumps turned on. When retarding the throttles lower than 15 inches of manifold pressure; the right engine failed; resulting in [requesting priority handling] with the tower and proceeding straight into Runway XX. After about 30-45 seconds with all engine controls in the full power position (throttle; propeller controls; and mixtures) the right engine started producing power again; but any power reduction below 15 inches of manifold pressure would cause the engine to sputter as if it would shut down again. Aircraft was brought over the runway and right engine power was only reduced once we were sure we could make the runway with no further incident. Once on the ground; the engine was able to maintain power with no further incident. Inspection of the bottom of the engine cowl by the cowl flap showed fresh oil that has been blowing backward under the wing. My student and I then removed the upper engine cowl; and saw no visible oil on the engine; magnetos; etc; but did see oil resting on the lower engine cowl inside the engine compartment.