You're probably right that not a lot of folks run 15" PA speakers with their modelers. Apparently Liam and I do (and the same one). I've been running two F115s (usually not at once) and two fEARful 15/6/1's for some time now. There's an F112 (and an F110, for that matter) that subs in a 12" speaker and is smaller overall, weighing in at around 35 lbs. Honestly, I think an F112 could do me for most gigs. It's not "extra bass response," however, that the F115 (15") provides, but increased volume. You get the same bass response from the F115, the F112 and the F110. I bought mine when I was looking for a full-range flat response bass cabinet that was a LOT lighter than your usual 4x10. I discovered that it was perfect for keyboards as well, and it's now become the guitar thing, too. The F115 isn't big -- around 26"H, 20"W, 16.75"D and weighs just over 40 lbs (mine's under 45). They're slightly larger but definitely lighter than most 2x12s (Orange and Mesas weigh in at around 65-70 lbs).That's pretty notable for a cabinet that will handle nearly 900W. My Korg keyboards use all of the F115, and it never farts out. I use a Helix and a Variax JTV-89F with it as well, and the alternate tunings on the Variax are very happy with it.