IMO one 15 could get louder the 2 12's i see this a ton on this site im not talking sh*t just saying everyone says 2 12's will be louder cause of more cone area that is so not true my friends one 15inch HD out did you 15inch HDs its all on your box design an the power your running id say either way you go you would be happy me id do the 15" BL casue 15's can pick up lower notes that 12's cant inless your running a van like assmans with like 20+10's its all up to you man