When you're dividing exponents, you subtract. The numbers act the same however, so you can divide the values separately and then put them together at the end.
15 ÷ 3 = 5
x^6 ÷ x² = x^(6-2) = x^4
y³ ÷ y^8 = y^(3-8) = y^-5
So your final answer is 5x^4y^-5
I hope this helps!