How to increase comment length?

Solved the issue. Thank you @birgire for giving me a hint. First I edited MySQL wp_comments table by changing comment_content rows «Type» from TEXT to MEDIUMTEXT and restarted MySQL. Then created filter in functions.php:

add_filter( 'wp_get_comment_fields_max_lengths', 'my_length' );
function my_length ( $lengths ) {
global $wpdb;

    $lengths = array(
        'comment_author'       => 245,
        'comment_author_email' => 100,
        'comment_author_url'   => 200,
        'comment_content'      => 16777215, //it was 65525
    );
    return $lengths;
}

and it worked 🙂 but let me know if I can make the filter more simpler? without array?! Thank you.