I use these shell scripts for generating passwords. This uses bash.

  gen-pass(){
    gpg2 --armor --gen-random 1 15
  }
  gen-pass2(){
    openssl rand -base64 15
  }
  gen-pass3(){
    strings -n 1 < /dev/urandom | tr -d '[:space:]' | head -c15
    echo ""
  }

edit:formatting