A 215 is constructed with MDF for cab back, baffle board, and separator plank. The cab sides are plywood. (Not sure about the top -- don't feel like yanking driver to find out.) How do I know this? I have the top half of a 215 sliced in two just below its mid point, i.e. separator board upwards. I converted it to sealed. Frickin' thing weighs a ton even empty. The original 2x15 weighed two tons. I bought it in the mid to late '70s. Wish I'd bought the D variant instead but the D was slightly more and I was broke at the time. I have a Peavey Pro 15 in it now, which does a credible job, especially at around seventy-five bucks, and I'd rate it somewhere between the original square-magnet job that came with the cab and a BW.
Last summer I heard, outdoors, a TNT combo with a BW, and it was able to get ungodly loud and stay clean at the same time. Impressive. Makes me think maybe I should stick a 1508sps into this Peavey box, except my Avatar B212 cabs each weigh less and could probably at least match its output, especially down low, so there'd be no point to the exercise.