I have about 2 million pages on my website (Wordpress) . The google is always crawl many pages on my website (recrawl old pages) and recently it took about 3 days to index the new pages in order to show in google result.
How to stop recrawl?
Sample of my sitemap : http://www.serze.com/post_part1.xml
Discourage search engine from indexing choice is your entire site will make non accessible for google. Your website wont rank on search result after that.
You can set update frequency for specific pages on your sitemap.xml.
https://www.sitemaps.org/protocol.html (check changefreq and priority tag)
Also you can check crawl stats on search console. https://support.google.com/webmasters/answer/48620?hl=en
But it might be different problem. Did you anything for seo or software updates?