So the tower of victory says that it should increase attack speed by 15% if you click on it. However, if you check the units, it says they are getting 20%.
In the PUP it was nerfed from 20% to 15%, however that was not shown in the final patch notes for season 5.
So it may just be they were going to change it and then decided not to, but they left the tooltip wrong on the landmark.