Required sum = (2 + 4 + 6 + ... + 30)

This is an A.P. in which a = 2, d = (4 - 2) = 2 and l = 30.

Let the number of terms be n. Then,

t_n = 30 ==>    a + (n - 1)d = 30

==> 2 + (n - 1) x 2 = 30

==> n - 1 = 14

==> n = 15