/**
 * @snippet       Maxlength @ WooCommerce Checkout Field
 * @how-to        Get CustomizeWoo.com FREE
 * @author        Rodolfo Melogli
 * @testedwith    WooCommerce 4.5
 * @donate $9     https://businessbloomer.com/bloomer-armada/
 */
add_filter( 'woocommerce_checkout_fields', 'bbloomer_checkout_fields_custom_attributes', 9999 );
function bbloomer_checkout_fields_custom_attributes( $fields ) {
   $fields['billing']['billing_company']['maxlength'] = 15;
   return $fields;
}