Code improvement advices

try {
            DB::transaction(function () use ($file, $file_name, &$ship) {
                $ship = Shipment::create([
                    'filename' => $file_name
                ]);

                $all_stored_product_serials = Product::distinct()->pluck('serial')->toArray();
                $all_stored_product_mfg_serials = Product::distinct()->pluck('mfg_serial')->toArray(); 
                Excel::toCollection(new ProductsImport($ship->id), $file)->first()->map(function ($import) use ($ship, $all_stored_product_serials, $all_stored_product_mfg_serials) {
                    $import = $import->toArray();
                    unset($import['id']);
                    $import['serial'] = trim(strtoupper($import['serial']));
                    $import['mfg_serial'] = trim(strtoupper($import['mfg_serial']));
                    // $import['category'] = $import['category']  ?? '';
                    $import['shipment_id'] = $ship->id;
                    $import['created_at'] = now();
                    $import['updated_at'] = now();

                    $import['sku'] = $import['serial'] ? trim(strtoupper($import['sku'])) : ''; // temporary sku until generated after loop to decrease querires
                    if (
                        in_array(strtoupper($import['serial']), $all_stored_product_serials) ||
                        in_array(strtoupper($import['mfg_serial']), $all_stored_product_mfg_serials)
                    ) {
                        Duplicate::insert($import);
                    } else {
                        Product::insert($import);
                    }
                });
                $this->generateSku($ship); // <===== Not called why ?
            });

            $message = 'File uploaded successfully';
            return redirect('/shipments/' . $ship->id)->with('success', $message);
        } catch (\Exception $e) {
            $message = 'Unexpected error happened';
            return back()->withErrors('', $message);
        }
    }

    public function generateSku($ship)
    {
        $sku_start_number = 100001;
        $all_stored_product_names_skus = Product::distinct()->pluck('product', 'sku')->toArray();

        $shipment_products = Shipment::find($ship)->products;

        foreach ($shipment_products as $product) {
            if ($product->sku == '' || $product->sku == null) {
                // if the name already exists in the db - get the same sku
                if (array_key_exists(trim($product->product), $all_stored_product_names_skus)) {
                    $product->sku = $all_stored_product_names_skus['product']; //sku from arr by product name
                } else {
                    $type_2letters = $product->type ? substr(trim($product->type), 0, 2) : 'PR';
                    $brand_2letters = $product->brand ? substr(trim($product->brand), 0, 2) : 'BR';
                    $sku_start_number += 1;
                    $sku = $type_2letters . $brand_2letters . $sku_start_number;
                    $product->sku = strtoupper($sku);
                    $product->save();
                }
            }
        }

        $ship->ended_at = now();
        $ship->save();
    }

Without using Quoues: I tried to decrease the queries to the fewer amount but the upload time is still the same , any improvement Is appreciated

also, i do not know why the generateSku function was not called or executed. + the page not redirect ...

should I upload via ajax ?