Answer:
10moles of kcl
Explanation:
2 K C l O3 →  2 K C l  +  3 O 2
Notice that you have a  2 : 3  mole ratio between potassium chlorate and oxygen gas, which means that, regardless of how many moles of the former react, you'll always produce 2/3 times more moles of the latter.
15 mol of O2 * ((2mol of KCLO3)/(3mol of O2))= 15*2/3=10 Mol