So I am making a diorama shelf to hold my 1/24 cars and to display them in a creative fashion. I know nothing about shelf bracket strength, so please help me out.

This board, which is a ambitious 4' by 15", is pretty heavy, so I’m thinking of getting some heavy duty shelf brackets. This link, says that these peculiar brackets can support up to 250 lbs evenly. So does that mean I need two to evenly distribute the weight, which adds up to 250 lbs (I think I read that right)? And I believe 3 brackets (if possible) would be better, right? If you have any other input that you feel is useful, don’t be afraid to share. I want to get this right the first time, :).