How long does a 15|10 Tournament(5 Rounds) usually lasts?

How long does a 15|10 Tournament(5 Rounds) usually lasts?

15/10 game usually can last about 25 minutes.  5 rounds can last about slighty over than 2 hours.  You might want to make it 2 hours 30 minutes.  

About 35 minutes a round is more realistic. 
a 5 round 15 / 0 tournament is about 3 hours long. 

Let's say that at the end of a 40-moves long game (the longest per round), both players have about 3 minutes.

24min + 80×10sec (800sec = 13min) = 37min.

37min × 5 = 185min = 3h 5min

Seriously, 3 hours?  I have never played one that long.  Anyway, 3 hours for 5 rounds should be safe. 

Thank you all.

plus 10-15 min time interval after each game for the pairings and board placements.