storefront-per-section.php

add_action( 'customize_register', 'jp_override_storefront_powerpack', 21 );
/**
 * @param WP_Customize_Manager $wp_customizer
 */
function jp_override_storefront_powerpack( $wp_customizer ) {
    $controls = array(
        'sp_homepage_featured_products_limit',
        'sp_homepage_top_rated_products_limit',
        'sp_homepage_on_sale_products_limit',
        'sp_homepage_recent_products_limit',
        'sp_homepage_category_limit',
        'sp_homepage_best_sellers_products_limit',
    );

    foreach ( $controls as $control ) {
        $control_object = $wp_customizer->get_control( $control );
        if ( ! $control_object ) {
            continue;
        }

        for ( $i = 13; $i < 25; $i++ ) {
            $string                             = (string) $i;
            $control_object->choices[ $string ] = $string;
        }
    }
}