If you have an equation and you need to find y intercept you have to plug in 0 where ever you see a "x"
y = 15(0)
y = 0
In this case the y-intercept is (0,0)
You could also graph the equation and it would look like this:
As you can see the line crosses (intercepts) the y-axis at (0,0)
I hope this helped!