OK, I don't have any photo evidence to point this out, but I've been experimenting with the 915 and 476 for a couple of weeks now and I wanted to point out my observations.
First, I've used both of these on a variety of finishes and colors, all generally prepped the same way over ten different vehicles.
The 915 is even harder than the 476 out of the tin. Really, it's like a solid chunk of plastic! The only way I could get it to spread was to let it sit in the sun with the cap off to warm up, then blowdry the top of the can until it started to "melt" a little. The 915 smells better than the 476, if that's an issue.
The 915 needs to go on even thinner than the 476. Seriously, you need to work it in to where it's the consistency of Crisco or you will never be able to get it off. Also, unlike the 476 you have got to do it one panel at a time. The 476 I can do the whole car, if it's not in direct sunlight, and let it sit overnight. Not so with the 915.
Even though it's been derided previously in another thread, and I was skeptical myself, the best method I've found for applying the 915 is literally by hand. Once it's warm enough grab a chunk and work it through your hands like you were drying your hands under an automatic hand dryer. This will thin it enough to the consistency you need to work with. The on can directions state that you should apply it with a damp cloth. DO NOT attempt this unless you want a big smeary mess on your hands. The wet cloth approach works well on wood and plastic, though. You should make sure your hands are clean and dry before doing it, the less oil from your hands the better.
Application is definitely easier with the 476s, but the 915 can be easier to take off if you do it panel by panel. The 915 is more forgiving on rubberized and plastic trim than the 476 is. The 915 takes to chrome and aluminum very poorly, but the results are shinier. However, when it comes to repelling brake dust off of wheels, the 476 has it beat.
If you use wax on exterior glass like I do, I'm liking the 915 over the 476. It actually seems to remove slight haze and nicks (ok, maybe it's just covering it up) and it does come off eventually with some Windex and elbow grease, unlike the 476s which seems to make a symbiotic attachment to the glass and refuses to let go.
Now for the looks department. I would say that 8 out of 10 vehicles look better with the 915 over the 476s. The shine, depth, gloss, wetness, etc from the 915 is incomparable. The 476 is no slouch in this department either, as it's taken the place of nearly every other wax I've used in the last twenty years. Previously that title was held by Meguiars Yellow 26, which I will still use when wanting a liquid versus paste wax.
I will say that if your paint is neglected, or non-clearcoated, use the 476s. You will not benefit from the extra "pop" that you would get from the 915. As far as a modern, good condition finish, try the 915, especially for a darker vehicle. If your paint is a light silver or beige with some metal flake, the 476s brings the flake out more. The darker the paint, the opposite is true with the 915.
On my plain white cars, the 915 brought out a depth that I don't think was there even when it was new. I initially expected the opposite, as it's generally accepted that a wax that benefits darker paint with some flake would not be as warm on a flat light finish. That's simply not true with the Collinite line.
As for Durability, I believe the 476s will win that race given time. Two 1996 Centuries with the same paint condition, one got a single coat of 915 and the other 476. Both are stored outdoors. After two weeks, the 476 has lost absolutely none of the beading abilities. The 915 has lost a little bit of its water sheeting, so I believe for the best durability out of the 915 a second coat could be more beneficial. Based on my other experiments, two coats of 915 = one coat of 476s. Either way, they're both extremely durable.
So, bottom line for me is that these are two incredibly great waxes. I believe that I favor the 915 moreso than the 476s. I'm stunned with the looks from the 915, and I believe if you're a fan of the 476s then come the warmer months try a little 915 in your wax regimen, you may be pleasantly surprised. I got mine off of ebay for 22.50 shipped, compared to the 13.50 for the 476s from the same dealer. (Harbor Freight is 14.00 on the 476 and 23.00 for the 915, so I actually save money getting it off Ebay.)
I've been reading for awhile that they were both essentially the same wax with a different smell, but I can say that they're two similar waxes with two different results. Either way, two cans should last me several years judging by the amount I've used so far!