wp-includes/rewrite.php(788) Slow down website with a lot of pages

Hello everyone.
I’m trying to resolve the following issue. I’m currently working on a website with 700+ pages using the following permalink structure: /%category%/%postname%.

The pages are all saved under one parent like:

/Parent
|—page
|—page1

Using the excellent WP Tuner plugin I tracked down the problem to the following:

5) Query: [wp-includes/rewrite.php(788): wpdb->get_results()]
SELECT ID, post_name, post_parent FROM wp_posts WHERE post_type = ‘page’
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE wp_posts ref type_status_date type_status_date 62 const 957 Using where
Query time: 8.5610 (ms)

Tried:
Deactivating the permalinks the problem goes away but off course this is not the ideal solution.
DB Cache Reloaded and WP Super Cache sadly are not useful for this issue.
There is no load on the server

I would like to know if it’s possible to speed up that query or if it’s possible to hard code the results of that query. In fact the page list is not going to be increased any time soon so I can just add the new query result when necessary.

Thanks for your time ??