Search with quotation marks is slow

Not really. Doing a phrase search is much, much slower, as the database server has to look inside every post, and that’s very, very slow on a big site like yours.

You can add this function to your site to disable the feature:

add_filter( 'relevanssi_modify_wp_query', function( $q ) {
    $q->set( 's', str_replace( '"', '', $q->query_vars['s'] ) );
    return $q;
} );

Thank you for your quick response. Amazing 🙂
I gave it a try and now the search is a lot quicker.