<?php
if(date('m') >= 06) {
   $d = date('Y-m-d', strtotime('+1 years'));
   echo   date('Y') .'-'.date('y', strtotime($d));
} else {
  $d = date('Y-m-d', strtotime('-1 years'));
  echo   date('Y', strtotime($d)).'-'.date('y');
}
?>

2015-16