<?php

$data = Array(
    'sites' => Array(
        0 => '',
        1 => '5 Estacao',
        2 => '3 Estacao',
        3 => '4 Estacao',
        4 => '1 Estacao',
        5 => '2 Estacao',
    ),
    'IPs' => Array(
        0 => '',
        1 => '172.168.0.15',
        2 => '172.168.0.13',
        3 => '172.168.0.14',
        4 => '172.168.0.11',
        5 => '172.168.0.12',
    )
);

function order ($arr)
{
    $arr = array_map(null, $arr["sites"], $arr["IPs"]);
    
    usort($arr, function ($a, $b) {
        return strcmp($a[0], $b[0]);
    });
    
    return [
        "sites" => array_column($arr, 0),
        "IPs"   => array_column($arr, 1)
    ];
}

print_r(order($data));