The answer would be 5/8. Find the GCD (or HCF) of numerator and denominator
GCD of 15 and 24 is 3. Then you Divide both the numerator and denominator by the GCD
15 ÷ 3
24 ÷ 3
Your answer would be Reduced fraction:
5
8
Therefore, 15/24 simplified to lowest terms is 5/8.