The JVC wins here. It's pretty quiet overall. The InFocus is about average overall. In full power lamp mode, it just might bother the more audible noise sensitive viewers. In low power, where it's still about a bright as anything else, it's as quiet or quieter than the JVC at full power.
Audible noise should not be an issue for all but a very few. It was fine for me, in my main theater, sitting the usual 4 feet behind (and to the side) of my seat.
InFocus SP8602 vs. DLA-RS15 Special Features
While neither projector is dripping in features, they are fairly well endowed. Both offer CFI, dynamic sharpening, and a dynamic contrast control Of course the JVC does not have a dynamic iris, which the InFocus offers. Both also use Frame Interpolation (non-creative) to speed up standard 24fps, to help minimize one type of motion blur, even when not using CFI. As you probably know, I don't get into a lot of little features, such as security features, sleep timers, etc. Both seem to have plenty of those types of features.
InFocus SP8602 vs JVC RS15 Bottom Line
Tough call. Really! I'd have to say choosing between these two will really come down to choosing which of these two, similarly priced projectors works best for your mix of content, your room, and other factors that are your preferences. Overall, one would have to consider them pretty close to a tie, due to some trade-offs.
That said, because of the brightness options, I would go with the SP8602 - if it would work in my room, for positioning purposes. In my current home, I could actually get the InFocus on my rear shelf. Of course that would be with the zoom at pretty much full telephoto, so it would cost me some lumens. Still, it would still be brighter than the JVC, because I could raise my shelf from 0 offset, to about 20 inches above, to get the extra 18% more lumens out of the InFocus. In other words, yes, I'd go with the InFocus. And that's not easy to say for someone who owned the original JVC - the RS1, which evolved into the RS15.
I'm moving though - in a few months. The theater in the new place just might work better for the JVC, though. As I said, placement may be a key factor in your decision.
Given either will work in your room, the big trade-offs are: InFocus advantage for sharpness, ultimately slightly better color accuracy, and brightness, vs. the JVC's slightly better blacks, smoother operation (no visible dynamic iris action, since no dynamic iris), power everything, and being physically more attractive.
What a tough choice, though it comes with a silver lining: Both are excellent projectors overall, and should satisfy all but the most hard core.