I recorded video of PTR and Live against the training bots and both killed the training bot in 7 seconds. Other people have done testing as well.
Edit: to clarify I tested only 1 turret on Live and PTR not all 3 for PTR or 6 for Live. So 1 single turret on both Live and PTR takes 7 seconds to kill a training bot.
Update: According to the latest patch notes they patched a “bug” causing symmetra turrets from doing the correct damage/slow.
So either there was an error with updating the turrets or we were just straight up lied to.