Speeding Up Bulk Post Creation - wp_insert_post & update_post_meta

I am creating posts (variable products) using (wp_insert_post) function. An Example, I have 9 colors, 9 sizes. Which makes 9×9 = 81 total variations for 1 product, which is 81 times below function to be executed.

function create_product_variation( $product_id, $variation_data){

    $product = wc_get_product($product_id);

    $variation_post = array(
        'post_title'  => $product->get_title(),
        'post_name'   => 'product-'.$product_id.'-variation',
        'post_status' => 'publish',
        'post_parent' => $product_id,
        'post_type'   => 'product_variation',
        'guid'        => $product->get_permalink()
    );

    // Creating the product variation
    $variation_id = wp_insert_post( $variation_post );

    // Get an instance of the WC_Product_Variation object
    $variation = new WC_Product_Variation( $variation_id );

    // Iterating through the variations attributes
    foreach ($variation_data['attributes'] as $attribute => $term_name )
    {
        //Only have 2 attributes, size and color.
        $taxonomy = 'pa_'.$attribute;
        update_post_meta( $variation_id, 'attribute_'.$taxonomy, $term_name );
    }

    // Prices
    $variation->set_price( $variation_data['regular_price'] );
    $variation->set_regular_price( $variation_data['regular_price'] );
    $variation->set_image_id($variation_data['variation_thumbnail_id']);

    $variation->save(); // Save the data
}

Before running the above code, I encapsulate the loop as below:

$productColors = array("siyah","kirmizi","bordo","haki","beyaz","antrasit","gri-kircilli","sari","lacivert","acik-mavi");
$Sizes = array("5xl","4xl","3xl","xxl","xl","l","m","s","xs");

  wp_defer_term_counting( true );     //Speeding Up Bulk Update Tricks    
  wp_defer_comment_counting( true );  //Speeding Up Bulk Update Tricks    


  foreach ($Sizes as $size){                                        //Create each variation    
      foreach($productColors as $color){    
          $existingVarId = $wpdb->get_col($wpdb->prepare( "SELECT child.post_id
                                                        FROM wp_postmeta AS child
                                                        INNER JOIN wp_postmeta AS parent
                                                          ON child.post_id = parent.post_id
                                                        WHERE child.meta_value = %s and parent.meta_value = %s
                                                        and child.post_id in (select id from wp_posts where post_type = 'product_variation' and post_parent = %d)", array( $size,$color,$post_id )));
          if(!isset($existingVarId[0]))
          {
            $varCount++;
            if (in_array($size, $oversize))
            {
                /* SKIP Beyaz - Kırmızı - Oversize*/
                switch ($model) {

                case "Kadın Tişört": $price = 49;break;
                case "Fermuarlı Kapşonlu Sweatshirt":$price = 134;break;
                case "Kapşonlu Sweatshirt":$price = 119;break;
                case "Sweatshirt":$price = 109;break;
                case "Atlet":$price = 49;break;
                case "Tişört":$price = 65;break;
                }
            }
            else
            {
                switch ($model) {
                case "Kadın Tişört":$price = 49;break;
                case "Fermuarlı Kapşonlu Sweatshirt":$price = 108;break;
                case "Kapşonlu Sweatshirt":$price = 94;break;
                case "Sweatshirt":$price = 84;break;
                case "Atlet":$price = 49;break;
                case "Tişört":$price = 49;break;
                }
            }

            $variation_data =  array(
                'attributes' => array(
                    'beden'  => $size,
                    'renk' => $color,
                ),
                'regular_price' => $price,
                'variation_thumbnail_id' => $productColorsAndIDs[$color],
            );

            create_product_variation( $post_id, $variation_data);
          }
      }

  }

  wp_defer_term_counting( false);         //Speeding Up Bulk Update Tricks
  wp_defer_comment_counting( false );     //Speeding Up Bulk Update Tricks

The creation process is getting slow everytime, even I am on a fast hosting (SiteGround GoGeek hosting plan.) Above code creates 1 product in 1-2 minutes, which is pretty slow, and most of the time, I get gateway 504 errors while running it.

How can I optimize it to work faster ? Deferring seems not affective at all.