Hi,
In your case I would strongly recommend using the index table engine feature. That alone will make the search a lot faster, especially if you have a lot of posts to search for. That number of posts should not be an issue, we are regularly testing on a database with 100 000 posts.
Once you have configured and generated the index, then make sure to to enable it, and that’s it. After that your seach queries should be a lot faster.