The probability it will rain of Hari Merdeka is 2/15. Since you are finding the probability that will be no rain on Hari Merdeka, you also need to find the part of 15/15 that is not 2/15. You can do this by subtracting.
15/15-2/15=13/15.
The probability that will be no rain on Hari Merdeka is 13/15.
