Slow Opencart

SELECT p.product_id, (SELECT AVG(rating) AS total FROM review r1 WHERE r1.product_id = p.product_id AND r1.STATUS = '1' GROUP BY r1.product_id) AS rating, (SELECT price FROM product_discount pd2 WHERE pd2.product_id = p.product_id AND pd2.customer_group_id = '1' AND pd2.quantity = '1' AND ((pd2.date_start = '0000-00-00' OR pd2.date_start < NOW()) AND (pd2.date_end = '0000-00-00' OR pd2.date_end > NOW())) ORDER BY pd2.priority ASC, pd2.price ASC LIMIT 1) AS discount,(SELECT price FROM product_special ps WHERE ps.product_id = p.product_id AND ps.customer_group_id = '1' AND ((ps.date_start = '0000-00-00' OR ps.date_start < NOW()) AND (ps.date_end = '0000-00-00' OR ps.date_end > NOW())) ORDER BY ps.priority ASC, ps.price ASC LIMIT 1) AS special FROM category_path cp LEFT JOIN product_to_category p2c ON (cp.category_id = p2c.category_id) LEFT JOIN product p ON (p2c.product_id = p.product_id) LEFT JOIN product_description pd ON (p.product_id = pd.product_id) LEFT JOIN product_to_store p2s ON (p.product_id = p2s.product_id) WHERE pd.language_id = '1' AND p.STATUS = '1' AND p.date_available <= NOW() AND p2s.store_id = '0' AND cp.path_id = '728' GROUP BY p.product_id ORDER BY (CASE WHEN p.price IS NULL OR p.price = '' OR  p.quantity IS NULL OR p.quantity = '' THEN 0 ELSE 1 END) DE SC,  (CASE WHEN special IS NOT NULL AND special > 0 THEN special WHEN discount IS NOT NULL AND discount > 0 THEN discount ELSE p.price END) ASC, LCASE(pd.name) ASC LIMIT 0,15;