Every additional resource (stylesheet, script, image, video, etc) that a browser needs to load adds to the page's loading time. So the Launch script, being a script, will add to the page load time too. However, it's usually a very, very, very small amount of time.
Having said that, if you have a lot of marketing tags in Launch, then those too will add to the page load time, because they load even more scripts. So if there's any slowdown in page load time, it's not necessarily fair to blame Launch alone, but to look at all of the tags that you're loading too.
Page load time is one factor taken into search engine ranking, but it is one out of a whole lot of other factors. It would be foolish to blame low search engine rankings on page load time alone.
