Good question, in 2010 Google said that they "... today we're including a new signal in our search ranking algorithms: site speed. Site speed reflects how quickly a website responds to web requests." [1]

I believe that page speed is also important, google provides PageSpeed Insights to help you improve your site. [2]

[1] https://webmasters.googleblog.com/2010/04/using-site-speed-i...

[2] PageSpeed Insights https://developers.google.com/speed/pagespeed/insights/