Why is the math.random not choosing a number between what I tell it too?

When I run this code y is always a number that is below 5 and sometimes higher than 15

local y = math.random(5,15)
local i = 0
for x = 5,y do

i = i + 1

stats.Views.Value = stats.Views.Value + 1

script.Parent.Parent.Parent.no.POT.Text = "Views: ".. i

wait(0.6)

end