1/7 has an infinitely repeating decimal block of .142857 as its decimal expansion.
1/7 = .142857142857 ...
The repeating block has 6 digits in it. Note that the 7th digit of 1/7 is 1 which is the first digit of the repeating block.
To get the 2015th digit, divide 2015 by 6 and focus on the remainder.
2015/6 = 335 with a remainder of 5.
The 2015th digit of 1/7 will be the fifth digit of the repeating block 142857 which just happens to be 5.
Answer: 5