Goals by Ray O'Sullivan and Jack Kelly secured the win after the Austrians bagged an early goal.
Austria got off to a strong start when they opened the scoring with a long range effort in the eighth minute.
Ireland had the ball in the Austrian net in the 18th minute but the goal was flagged offside before Ray O'Sullivan turned the ball home.
O'Sullivan and Barry Coffey both had half-chances before O'Sullivan headed the equaliser in the 26th minute from a Callum Thompson cross after a quickly taken free-kick.
In the 33rd minute Sean Mahon Brennan's cross was narrowly missed by Coffey and three minutes later a cross by Max Murphy was flicked on by Adam Idah and forced a save.
Two minutes into the second half Oliver Wieneritsch fired narrowly over for Austria but Ireland soon got a grip of the game and Adam O'Reilly and Thompson both came close to putting the Irish ahead in the opening minutes after the restart.
In the 55th minute Ciaran Brennan did well to create a chance for Jack Kelly but his low effort was narrowly off target with Tyriek Wright getting close to connecting.
Five minutes later Kelly set up Ciaran Brennan but he fired just wide and within 60 seconds Thompson also had an effort fly wide from 20 yards out.
Austria hit an Irish upright in the 68th minute but the Irish bounced back with Wright just failing to hit the target.
Kelly's cross was headed over by Wright with four minutes left then Thompson led a swift counterattack which ended with the Austrian keeper making an important save.
However the keeper was lucky to escape with an error in the 79th minute when he failed to hold a Ciaran Brennan header and then Ireland went on to grab the winner in injury time when Kelly finished off an Irish move by rounding the keeper to fire home.
REPUBLIC OF IRELAND: Kian Clarke, Jason Knight, Ray O'Sullivan, Nathan Collins, Marc Walsh, Barry Coffey, Sean Mahon Brennan, Adam Idah, Callum Thompson, Max Murphy, Kevin O'Reilly.
Subs: Harry Clarke for Clarke 41 mins, Jamin Nwanze for Murphy 41, Adam O'Reilly for Knight 41, Jack Kelly for Walsh 41; Tyriek Wright for Mahon Brennan 41; Ciaran Brennan for Idah 41; Oisin McEntee for O'Sullivan 41; Kameron Ledwedge for K O'Reilly 65; Sean Brennan for Coffey 65.
U15 International Tournament
Tuesday, February 2
Republic of Ireland 1-2 Netherlands
Turkey 3-0 Austria
Thursday, February 4
Republic of Ireland 0-1 Turkey
Netherlands 4-0 Austria
Saturday, February 6
Republic of Ireland 2-1 Austria
Turkey 0-1 Netherlands