Ignoring the weight of the mechanisms, the mechanical advantage is simply the ratio of the distances from the fulcrum to the load and from the fulcrum to the force. So if the press (the load) is 3 feet from the fixed end (the fulcrum), and the lever (the force) is 15 feet long, you'll get a 5:1 advantage. So you'll need to apply 300 pounds of force to get 1500 pounds of pressure.