2x + 5y = 15
      -2x       -2x
     ---------------
            5y = 15 - 2x

Write the second term first on the right:

            5y = -2x + 15

Divide every number by 5

           y = x + 

Simplify:
                                       
          y = x + 

            y = x + 3

That's the slope-intercept form,

            y = mx + b 

where the slope is m, which equals , and
the y-coordinate of the y-intercept is b, which equals 3.
That means the y-intercept is the point (0,3).

Edwin