I didn't use 4 15"s the other night, but I could have, I have a Sunn 215b and two Joe's 15" cabs. Friday night I used my 301 on my side of the stage and the 215b on the guitarist's side. One of the best bass sounds I ever got!
Don't be fooled by the guitarist's 12" Fender Hot Rod Deluxe. That is a very loud 40 watt guitar amp! He is an old rock'n'roller and plays pretty loud, the soundguy doesn't mike his amp usually. They didn't need to use too much of my direct signal, either! He likes to hear the bass so he was pleased with my setup. He also said something about bringing his Marshall stack.
I said "Bring it on!"