This value, in minutes, is the configured or actual length of the collection window for the 15-minute interval that is still actively accumulating right now. On this element it is what you divide the accompanying access-hit byte and frame counters by to turn a raw cumulative count into a meaningful average rate for the still-accumulating current interval, and it is also how you spot a truncated bin -- one whose Duration reads less than the table's normal interval because a clear or restart cut it short. For a normal Curr bin this should read 15; a value of 6 instead would mean the access-hit counters accumulated for only 6 of the expected 15 minutes, so any total should be scaled up before comparing it against a full bin.