What about something like this (assuming you're using bash):
dec=0.1; for i in {1..15}; do perl -ane 'BEGIN { $dec=shift }; print join( "\t", @F[0..2], $F[3]-$dec ), "\n"' $dec num_table.txt > file_$i.txt; dec=$(bc <<<$dec+.1); done
That will start with the decrement value of 0.1, and use a shell loop to create 15 new files with the last field modified by the decrement value, which is increased by 0.1 each time. I'm not completely clear on your desired format, but maybe this will get you started.