secondsElapsed was added in one of the 2.6 Beta Versions, so no, the last full version of TD2 was 2.5.11 (From memory)
Version 2 you could use:
Create a event, with The Tournament Starts as the trigger, play your first sound file.
Create a second event as follows:
Trigger: The Clock Ticks
Conditions: (isRound) and (state = 2) and (roundNum = 1) and (secondsLeft = 890)
That would give the same result, but your first round would have to be the same duration each time, for example if on one occasion you decided to go for 30 minute levels it would still fire with 890 seconds left in the first round.
SecondsLeft = minutes in level (say 15) X 60 - the seconds into the level you want it to fire, so for a 15 minute level with the event firing after 10 seconds it would be 15 x 60 = 900 - 10 = 890 seconds.
Regards
Stuart