SQL & PL/SQL

SELECT DISTINCT t.category_set_name, b.segment1, tl.inventory_item_id,
tl.category_set_id, tl.category_id FROM mtl_category_sets_tl t,
mtl_categories_b b,
mtl_item_categories tl
WHERE t.category_set_id = tl.category_set_id
AND b.category_id = tl.category_id
AND t.category_set_name NOT IN (
SELECT category_set_name
FROM mtl_category_sets
WHERE category_set_name LIKE
'BU_%');

I used sub query to neglect the records starts with "BU_ " but it performing very slow,Please any one help me out what i can use instead of sub query.

Thanks
Senthil