We loaded something like 150 million records from Library of Congress and had a co-located 2 post rack running a quad processor something-or-other with a RAID 5 setup on Oracle 8i. Users ranged into the thousands online at once doing queries. RPS peaked over 50 per second if memory serves (this was 1999).

We filtered stop words, and plurals, but not misspellings nor synonyms.

Using materialized views is very smart. Be aware of disk space with lots of records. I'm on a project now that has over a billion records in one table. We have to plan very carefully for index growth and maintenance (rebuilds). Adding a materialized view that copies and concatenates text columns (and then builds FTS indexes on that, which might be in addition to FTS indexes on individual columns) could take up considerable space.

For 15 million records with an average row length of 65 characters you're talking close to a gigabyte of space for the materialized view. Not a problem for an in-house server, but for a hosted server or a cloud database, that could cost you actual coin per month.

My point there isn't to talk you out of materialized views. I love that idea. Just look at the whole picture when designing things, and plan for growth/scale.