Dominique is making a rice dish for 5 people that requires 4 teaspoons of salt. If she were to add just one more teaspoon of salt to the rice after tasting it, half of the time she would be able to notice a difference. If Dominique decides to triple her recipe to feed 15 people, which would call for a total of 12 teaspoons of salt, how many teaspoons of salt would need to be added for a person to be able to taste the difference half of the time?