I think that as far as an aluminum alloy wheel goes, it's going to depend on how the wheel is constructed. Inexpensive alloy wheels are typically not build for strength, they are built down to a price. An alloy wheel like a Method, or other high quality wheel would likely serve most people just fine, but the $200+ per wheel price point is what probably scares most people away. Forged alloy wheels are very strong and in some cases may actually take more force to deform, or break than a steel wheel, now if the wheel becomes too deformed to allow the tire to stay seated or hold air pressure, you still would not be able to perform a trail repair. Steel wheels can also vary in quality based on price, but typically the gap from a "high end" steel wheel to an inexpensive steel wheel is small. As mentioned above, weight savings based on wheel size is going to be minimal, but also take into account that wheel and tire combination weight is all rotating mass, and has a large effect on "butt dyno" and potentially braking distance/feel as well. 15" sizes are being phased out due to newer vehicles typically having 16" or larger wheel sizes, thus making the tires for the larger wheels usually cheaper and potentially easier to source in the case of an emergency. I think the question of wheel size and construction material comes down to more personal preference and your terrain and driving style. If you find yourself in rocky or rough terrain and you like the use the skinny pedal, steel wheels would probably be a safer bet. If you find yourself daily driving your rig and taking easier terrain and being more precise in your vehicle control, then an alloy wheel may suite you better. One major thing to consider no matter what wheel construction you choose, is to be sure that the fitment is correct, and usually if you like to run low air pressure (read 10psi or less) then pick a wheel that has a width that is more on the narrow side for the tire size you have chosen, this will typically help keep the bead of the tire seated on the wheel in low air pressure situations. I used to run 31/10.50r15 on a 15x8 steel wheel at 6-8psi in the snow and never had an issue with debeading a tire. I switched out to 33/12.50r15 with alloy wheels 15x10 (i think they were american racing, but i don't remember) and had to keep the air pressures above 12psi in the snow to keep the tire from bebeading.