Join query on 1M row table slow

I have a pretty simple select query that joins a table
(p) with 125K rows with another table (pc) with almost
one million rows:

select p.*
from product_categories pc
inner join products p
on pc.product_id = p.id
where pc.category_id = $category_id
order by p.title
limit 25
offset $offset

The query usually takes about five seconds to execute
(all other PG queries perform fast enough). I have
indexes on everything needed, and EXPLAIN shows
they're being used. Is there anything else I can do to
improve performance - such as tweaking some settings
in the config?

Redhat 9, PG 7.4.1.

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