This read-only Unsigned32, in joules per its source description, reports the energy this PoE port supplied to its attached device over the most recent 15-second window, automatically updated at that interval. Admins use this slightly longer window than the 5-second figure to smooth out very brief spikes while still catching short-term power usage patterns. For example, comparing the 5-second and 15-second readings for the same port helps an admin tell whether a power spike was a brief blip or part of a sustained draw.