If a solution has a pH of 1.5 it's an acid, meaning that it contains more H+ ions than OH- ions. A solution with pH = 7 is neutral. It has equal concentrations of H+ and OH- ions. In order to neutralize the acid, you would need to add a base, which is a solution with an excess of OH- ions. Without knowing the volume of the pH 1.5 solution you can't calculate how much or what concentration of base to add, but if you have a pH meter or pH indicating paper you could add base until the pH reaches 7. A common base is aqueous sodium hydroxide solution. In areas where acids are used there are usually acid spill clean-up kits that contain solid sodium carbonate or sodium bicarbonate, both weak bases, to neutralize spills.