Page load speed has been a ranking factor with Google since some time. It was mainly a signal for desktop users. Google has announced that it will be the same for mobile users as well
Although speed has been used in ranking for some time, that signal was focused on desktop searches. Today we’re announcing that starting in July 2018, page speed will be a ranking factor for mobile searches.
The “Speed Update,” as we’re calling it, will only affect pages that deliver the slowest experience to users and will only affect a small percentage of queries. It applies the same standard to all pages, regardless of the technology used to build the page. The intent of the search query is still a very strong signal, so a slow page may still rank highly if it has great, relevant content.
You can use Page Speed Insights or Lighthouse tests to find out how your site fares in Google search on the speed litmus