In a regular polygon, all sides are same size and measure of all interior angles are same.
The sum of interior angles of polygon of 15 sides is
(n−2)×180o where n is number of sides of polygon.
(15−2)×180o=1440o here n=15
Each interior angle =2340/15=156o
As we know that the sum of interior and exterior angles is 180o
Exterior angle + interior angle =180o
Exterior angle +156o=180o
Exterior angle =180o−156o=24o