Website loading times are considered a key part of user experience, which in turn is a central plank of SEO performance.
However, it is unlikely that a website will receive a direct penalty as a result of having slow page loading times. Only a very small number of websites have ever received a penalty for this reason. It is much likelier that slow loading times will simply prevent you from reaching as high a position in the search engines. This is because most of the websites that suffer from slow loading times are relatively new, so don’t have as much authority in the eyes of Google yet anyway.
Of course, if you’re a well established site and you suddenly start having consistent problems with loading times, you could well see a penalty coming your way.