Durability can vary wildly from one location to another due to conditions, so without doing some testing yourself, it would probably be impossible to say for sure what to expect. I don't think you can go wrong with either product from Collinite. If you search around here, you can find some old durability tests on either of those. Almost certain 476S outlives 915 more often than not, though I recall at least one test in which the results were opposite. I have collinite 476S on one of my vehicles that has been in place for almost 5 months now, but I use spray wax over it as a booster, so however long it lasts wouldn't be a real indicator of what it can do on it's own in my climate. With either of those waxes, apply them as thin as possible or they will be a chore to remove. I like applying via machine because you can put extremely thin and even coats on that way.