How to speed up CSV generation?

Question

I'm trying to generate a CSV but its taking too much time. I have also specified the cols. I want in the query still the generation is very slow, how to speed it up ? Any suggestions will be appreciated. My php code is following, Thanks in advance.

$strdate = strtotime($_POST["strdate"]);
$enddate = strtotime($_POST["enddate"]);
    
$q0 = "SELECT ordr_id, ordr_cust_id, ordr_b_company, ordr_shipping_selected, ordr_timedate FROM shop_orders WHERE 
            ordr_ship_id = " . fix($_POST["sid"]) . " AND 
            ordr_timedate BETWEEN " . fix($strdate) . " AND " . fix($enddate) . " 
            ORDER BY ordr_timedate DESC";
$r0 = mysqli_query($conn, $q0) or die("Query Failed: Get Orders");
    
    if (mysqli_num_rows($r0) <> 0) {
        $prodtype = array("Consumables", "Materials");
    
        $csvfile = "orders-by-supplier.csv";
        $file = fopen($csvfile, "w");
    
        // Save headings alon
        $HeadingsArray = array(
            "Date",
            "Order #",
            "Customer ID",
            "GL Code",
            "Company",
            "SKU",
            "Part #",
            "Name",
            "Cat",
            "Size",
            "Price",
            "Qty",
            "Total",
            "Supplier"
        );
        fputcsv($file, $HeadingsArray);
    
        // Save all records
        while ($a0 = mysqli_fetch_array($r0)) {
    
            $q2 = "SELECT cust_gl_code FROM shop_customers WHERE cust_id = " . fix($a0["ordr_cust_id"]) . " LIMIT 1";
            $r2 = mysqli_query($conn, $q2) or die("Query Failed: Get Customer");
            $a2 = mysqli_fetch_assoc($r2);
    
            // Get Order Content
            $q1 = "SELECT orcn_prod_code, orcn_prod_part_num, orcn_prod_name, orcn_prod_type, orcn_option_0, orcn_price, orcn_qty, orcn_total  FROM shop_orders_content WHERE orcn_ordr_id = " . fix($a0["ordr_id"]);
            $r1 = mysqli_query($conn, $q1) or die("Query Failed: Get Order Content");
    
            while ($a1 = mysqli_fetch_assoc($r1)) {
                fputcsv($file, array(
                    date("d-m-Y", $a0["ordr_timedate"]),
                    $a0["ordr_id"],
                    $a0["ordr_cust_id"],
                    $a2["cust_gl_code"],
                    $a0["ordr_b_company"],
                    $a1["orcn_prod_code"],
                    $a1["orcn_prod_part_num"],
                    $a1["orcn_prod_name"],
                    $prodtype[$a1["orcn_prod_type"]],
                    $a1["orcn_option_0"],
                    $a1["orcn_price"],
                    $a1["orcn_qty"],
                    $a1["orcn_total"],
                    $a0["ordr_shipping_selected"]
                ));
            }
        }
    
        fclose($file);
    }