This will vary between browser/platform and between your connection speed. On my imac in Chrome with a fast connection the page scrolls ok.
However there is an inherent issue in all these scroll effect pages as they hijack the scroll event and rely on blisteringly fast machines to achieve their effects.
What I usually do is go back to basics and start at the beginning with a reduced test case and then gradually add features to see when the bottleneck occurs. If possible you should check other sites built on the code you are using to see if they have the same issues as yours and if not then that may alert you to look elsewhere for the problem.
Some browsers are better than others and IE/Edge always had mouse scrolling problems so if Edge is your problem then do a google search for Edge scrolling problems.