I am going to say the same as Alan and the video clip LOL
1024 is the biggest power of 2 that goes into 2015, so I will start there
2015
= 1024 with 991 remaining
=1024+512+479 remaining
=1024+512+256+223 remaining
=1024+512+256+128+95remaining
=1028+512+256+128+64+31remaining
=1028+512+256+128+64+16+15remaining
=1028+512+256+128+64+16+8+7remaining
=1028+512+256+128+64+16+8+4+3remaining
=1028+512+256+128+64+16+8+4+2+1
$$\\=2^{10}+2^9+2^8+2^7+2^6\qquad+2^4+2^3+2^2+2^1+2^0\\
=11111011111$$
Of course you could just use this converter
http://www.binaryhexconverter.com/decimal-to-binary-converter