You would need to find the percent of 2/3 so you divide 2 by 3. You should get 0.66 repeat. Then, you multiply 15 by 0.66 (nothing else) and get 9.99999 (10).
SECOND METHOD:
15 divided by 3 is equal to 5. Because 2 is the denominator, you would multiply 5 by 2 and get 10.
Hope this helps!