When comparing decimals, you have to compare each place value. Begin with the tenths place and compare each number that occupies that place. If they are the same, move to the hundredths place and compare. When you reach a place value where the numbers are not the same, compare them. The larger number in that place value is the larger number.
For your choices, when we look at the tenths place, we see that one of the numbers is 0 and all the other numbers have a higher number so we don't have to go any further...
c)0.015 is the smaller number