A Q400 flight attendant described the physical fatigue effect of a fifteen and a half hour day.

Narrative

Looking back on this day I am almost certain I was suffering from fatigue; I felt as if once in flight I hit a 'wall' having to work twice as hard to be alert and awake. I and the other Flight Attendant observed we were tripping on things we normally would have noticed and I was having to double; triple and quadruple check simple tasks to ensure I was properly completely my duties. Prior to leaving I was tired and discussed with crew the possibility that after leaving on our last flight that THEN we would really start to feel the effects of a 15.5 hour day. Upon further reflection on the trip; and how hard simple tasks became I became aware I was probably fatigued on the flight to ZZZ. It was a scheduled 12 hour day. We were delayed due to a mechanical on the plane we were scheduled to deadhead on. After a plane swap we departed at 2.5 hours late. We then did a round trip almost three hours late; as there were no reserve crews to cover any flights that day. It was a turbulent flight both there and back due to storms. We then left to ZZZ three hours late as well. I think the scheduling of 15.5 hours is too long and potentially unsafe. I feel that when you factor in the early report time; plus factor in the drive to work and the time taken to get up and ready; that is an extremely long day. We should have been swapped out from the round trip and been on time to ZZZ.