Is this 15" subwoofer good?
Believe it or not, I have one of those.
Bought it in 1990 or so for $149 from DAK. I had it paired with a pair of Mininus 7's for a few years in the spare room and it wasn't too bad, for what and when it was. It added a nice low end to small speakers,and it prevented the bass from getting to (and there for overdriving) the small speakers. IOW, it did exactly what it was designed for and marketed to do.
But, to compare it to today's powered HT subwoofers is a joke.