grep!$s{$_}&!($s&8&&~$s&$_&7)&!(~$s&8&&$s&~$_&7)&&($z=$s^$_)&8&&(($z&=7)<3|$z==4),15,grep$_%3,1..14

##</code><code>##

0-8    11-1    7-15
 \    /    \    /
  10-2      13-5
      \    /
       14-4

##</code><code>##

grep
  !$s{$_}              # we have not been at $_ already
  &!($s&8              # prohibit the boat is on the right bank initially
       &&~$s&$_&7)     # and a move from left to right
  &!(~$s&8             # prohibit the boat is on the left bank initially
       &&$s&~$_&7)     # and a move from right to left
  &&($z=$s^$_)&8       # the boat moves
  &&(($z&=7)<3|$z==4), # with at most one passenger
  15,grep$_%3,1..14    # possible choices for moves