Smarter way to give out lowest value of ACF field

at the moment I use the following function to give out the lowest number of a ACF field. The code is working but not the smartest and most resource conserving way.

add_shortcode( 'LEASINGFAKTOR', 'leaserate_shortcode' );
function leaserate_shortcode () {
$args = array(
        'posts_per_page'=> -1,
        'post_type'     => 'fahrzeuge',
        'meta_key'      => 'leasingfaktor',
    );
    $low_rate_query = new WP_Query( $args ); 
    $rate = array();

    if( $low_rate_query->have_posts() ):
        while( $low_rate_query->have_posts() ) : $low_rate_query->the_post();
            $rate = get_field('leasingfaktor'); 
            if(isset($rate) && !empty($rate)){
                $rates[] = $rate; 
            }
        endwhile;
        $max_rate = max($rates);
        $min_rate = min($rates);

        endif; wp_reset_query();
        return $min_rate;
}

Any ideas on making it cleaner, faster, smarter?

Well, You can use get_posts instead of using WP_Query because you just need the array of post ids that you can use with get_field, and using get_posts you don't need to do a while loop, and wp_reset_query

Another improvement that you can do is to use, array_map instead of foreach because you're not trying to generate any HTML here or not doing anything complex. you're just trying to get an array of rates so array_map is better in this case and easy to use and the code will be short.

So your final code using get_posts and array_map will be like this:

/**
 * Shortcode function
 */
function leaserate_shortcode() {
    $query_args = array(
        'posts_per_page' => -1,
        'post_type'      => 'fahrzeuge',
        'meta_key'       => 'leasingfaktor', // phpcs:ignore WordPress.DB.SlowDBQuery
        'fields'         => 'ids', // We just need ids for our work.
    );

    /**
     * We will use get_posts instead of using WP_Query
     * Because it's easy to use in this case and $no_found_rows
     * is set to false that will give fast performance
     */
    $post_ids = get_posts( $query_args );

    // Set default min rate.
    $min_rate = 0;

    // Check if we found ids or not.
    if ( ! empty( $post_ids ) ) {
        /**
         * We don't need to do foreach or for loop here
         * We can use an array map and map the post ids array
         * with the values.
         * So we will have an array of rates in the result
         */
        $rates = array_map(
            function( $id ) {
                // we use using type transform using (int)
                // assuming returning value will be a number or string number.
                return (int) get_field( 'leasingfaktor', $id );
            },
            $post_ids
        );

        // Filter empty values and get unique values.
        $rates = array_unique( array_filter( $rates ) );

        // Check if the final array is not empty.
        if ( ! empty( $rates ) ) {
            $min_rate = min( $rates );
        }
    }

    return $min_rate;
}
add_shortcode( 'LEASINGFAKTOR', 'leaserate_shortcode' );