mkdir $(seq 1 15)

seq 15 -1 1 | xargs -I@ mv @_* @

seq 15 -1 1 | xargs -I@ sh -c 'mv @_* @'

seq 15 -1 1 | xargs -I@ sh -c 'mv -- "$1"_* "$1"' x-sh @

seq 1 15 | xargs -I@ sh -c 'mv -- "$1"_* "$1"' x-sh @

i=1
while [ "$i" -le 15 ]
do
    mv -- "${i}"_* "$i"
    i=$((i+1))
done

for i in $(seq 1 15); do
    mv ${i}_* $i
done

mkdir {1..15}

for i in {1..15}; do
    mv ${i}_* $i
done