At this point in the game, the turrets are completely useless. And that's mainly just because Riot buffed all the tank items. After a maximum of 10 minutes, any champion in the game can tank a turret. You're more safe behind a minion wave than under a turret. 20 minutes in the game and even Jinx can tank a turret while her team hits it. The new laser thing that was implemented this season hasn't improved the turrets it actually made them worse. That shield at the inner turrets is completely useless and the nexus turrets can't even kill a minion wave pushing the base.
Thanks Riot for making this game terrible.