s = """1111110000111111
1110110110110111
1101010110101011
1011100110011101
0001111111111011
1000110111110111
0100010011110000
0110000001111110
0111000000110110
0000100010010100
1110110011000111
1101111111100011
1011100110000011
1101010111100001
1110110110111101
1111110000111111"""
>>> [''.join(i) for i in zip(*s.split())]
['1111010000111111',
'1110001110110111',
'1101000110101011',
'1011100010011101',
'1101110001111011',
'1110111000110111',
'0000100000010000',
'0111110000011110',
'0111111001111110',
'0000111100110100',
'1110111110010111',
'1101111111000011',
'1011100100000011',
'1101010111100011',
'1110110110111001',
'1111110000111111']
Edit
If you indeed want a single string as your output, add one more join
>>> '\n'.join(''.join(i) for i in zip(*s.split()))
'1111010000111111\n1110001110110111\n1101000110101011\n1011100010011101\n1101110001111011\n1110111000110111\n0000100000010000\n0111110000011110\n0111111001111110\n0000111100110100\n1110111110010111\n1101111111000011\n1011100100000011\n1101010111100011\n1110110110111001\n1111110000111111'