SELECT tag.tag, object.id
FROM   object
JOIN   object_tag
    ON object_tag.id_object = object.id
JOIN   tag
	ON tag.id = object_tag.id_tag
WHERE  tag IN (
	SELECT 	tag.tag
	FROM	tag
	ORDER BY COUNT (tag) DESC, tag ASC
	OFFSET 0
	LIMIT 15
)
ORDER BY tag
LIMIT 5