How Page Speed as a Google Ranking Factor Works
john Mueller: "...the faster you make the site, the more people are going to stay on your site, the more they are going to do on your site, the more they tend to recommend it to other people, so indirectly it is a factor.
"The other part of server speed is more in regards to crawling, so how quickly we can crawl pages from your website, and that’s not directly a ranking factor, but it does affect how quickly we can pick up new and changed content on your site."
How Page Speed as a Google Ranking Factor Works