Slow query and high memory usage

When I create a new post, it really takes a lot of time, around 30+ seconds, and a lot of memory: 300MB+ RAM. Query Monitor reports one slow query from Urvanov Syntax Highlighter:

SELECT wp_posts.*
FROM wp_posts
WHERE 1=1
AND wp_posts.post_type IN ('post', 'page', 'attachment')
AND (wp_posts.post_status = 'publish'
OR wp_posts.post_status = 'future'
OR wp_posts.post_status = 'draft'
OR wp_posts.post_status = 'pending'
OR wp_posts.post_author = 1
AND wp_posts.post_status = 'private')
ORDER BY wp_posts.post_date DESC

I have over 8,000 posts in my database, so I think it may be why it takes so long, and uses a lot of memory.

After I save the new post, this is not called anymore, the page loads must faster, around 2 seconds, and the slow query is gone.