Slow SQL query

Hi,

New here at the forum (except for reading sometimes without being logged in) and need some help 🙂

I need to get a custom menu from another site (sharing the same MySql but different databases).

I’m doing it this way:

function get_main_site_menus($custom_menu) {

		global $wpdb;
		$mydb = new wpdb('root','xxx','xxx','localhost');

		$menu_items = '';

		$custom_menu_items = $mydb->get_results("
			SELECT p2.post_title, p2.guid
	            FROM wp_posts p1
	            LEFT JOIN wp_term_relationships AS TR
	            ON TR.object_id = p1.ID
	            LEFT JOIN wp_postmeta AS PM
	            ON pm.post_id = p1.ID
	            LEFT JOIN wp_posts AS p2
	            ON p2.ID = PM.meta_value
	            WHERE p1.post_type = 'nav_menu_item'
	            AND TR.term_taxonomy_id = ( SELECT wp_terms.term_id FROM wp_terms WHERE wp_terms.slug = '$custom_menu')
	            AND pm.meta_key = '_menu_item_object_id'
	            ORDER BY p1.menu_order ASC
			");
		if ($custom_menu_items) {
		    foreach($custom_menu_items as $custom_menu_item) {
				$menu_items .= '
<li><a>guid . '">' . $custom_menu_item->post_title . '</a></li>
';
			}
		}

		return $menu_items;

	}

The problem is that this slows down the page with about two seconds of loadtime. Why is this function or SQL query that slow? What can I do to improve it?

Thanks in advance for any help!