If we write 2/15 as 4/30 and 1/10 as 3/30, the answer becomes clearer because we're comparing two like quantities, 4 thirtieths and 3 thirtieths. It's like comparing $4 with $3 or £4 with £3 or even 4 apples with 3 apples.
Now we can see that 4/30 is bigger than 3/30 by 1/30; or we can divide 4 by 3 and get 4/3 or 1 1/3, so 4 is a third bigger than 3, because a third of 3 is 1 and 3+1=4.