This read-only Counter32 reports the total seconds in a completed historical 15-minute interval during which this congestion point was in any of the Normal, Low, Medium, or Severe states. An admin uses this as the denominator to compute the proportion of that specific past interval spent at each congestion level. A nncAtmCongStatsShortIntvlTotalSeconds noticeably less than the full 900-second interval length would tell an admin that interval's state (per nncAtmCongStatsShortIntvlState) was affected by a reset or time change and doesn't cover the full window.