The arrow has both diagonals drawn in its shaft and a straight line running from the tail to the tip. How many triangles are there in the arrow?

Head: 2 halves and the whole head, 3. Shaft: 6 smallest triangles, 2 triangles at the ends with their apex at the centre, and 4 halves of the rectangle cut off by a diagonal, 12. Total $3+12=15$.