For me it worked fine with:
load * inline [
F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12 F13 F14 F15
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
] (txt, delimiter is '\t');
store F1,F2,F3,F4,F5,F6,F7,F8,F9,F10,F11,F12,F13,F14,F15 from t into testtest.txt (txt);
therefore I think that your problem is different to the number of fields - maybe it's missing the fileformat (bolded above) or something within the data (any kind of special chars like an eof which breaks the process) or something similar. Which release do you use (mine is QV 11 SR12)?