>>and I didn't ask why
Probably best to ask. The only reason I can think of is that he had an old receiver without bass management so needed speaker-level wires to the sub (then on to his mains), got a new receiver which let him use a line level connection, but didn't get around to rewiring the mains to not go past the sub any more.
For 15 feet I guess even 16ga should be OK... resist the temptation to open the Monster reel just because you have it in your hands. That's how they win
Home Depot stays open late in many cities and I'm sure WalMart sells wire if you're desperate.
Just to be clear, there's nothing wrong with Monster products AFAIK, we just think they're kind of expensive and find their marketing pitches unusually slimy.
