That head is from around 1980. It still works so that answers the reliability question.
I have the same model that I got in 2012, and it's only now showing signs of needing service--a few capacitors in the preamp are bulging and the pots need cleaning but the power amp section is going strong. Many parts for these are still available from Peavey, and you can download the owner's manual from their website.
It's generally agreed that the MKIV was a big improvement and is one of those amps where everything was perfect, but the MKIII still holds up and has a ton of features. It's the kind of amp that's probably been dropped off the back of a truck a couple of times in it's life, but you'd never know it. Peavey's reputation for reliability and durability was built on these amps and especially the 400 series power amp section, which has been used in PA heads as well for decades.
The "Comp" in/out switch doesn't actually activate a compressor as we usually think of them. It's Peavey's legendary DDT speaker protection limiter. I recommend using it. If the light is on more than it's off, you should probably back off on the volume or the bass a bit. But it's hard to get that to happen on today's quieter stages--with the 215 this is a loud rig.
There were 2 main versions of the 215 cab back in the day. One wasn't as deep as the other but it's still a good cab.
The deep one is a monster that OWNED the late '70s and most of the '80s. LOUD and punchy as hell, and very hard to blow up.
This combination is actually what I borrowed to play my first ever gig on bass.
Enjoy!