Re: 15" Speakers?
15" Speakers can be real nice with the right amp. IF yoyu have lets say a 30W amp and you are having some issues with headroom a 15" Speaker can help this quite a bit. I'm not sure if its the size or the added wattage of the speaker that helps this. Some of the amps I have had some time on that came with 15" speakers are the Fender Dual Showman Reverb. This is essentially a Twin in a head and the stock bottom had 2 15" speakers in them. The bottom on these amps was very powerful and thes amps were very loud yet very clean.
Another great amp that had a 15" was the BF Vibroverb. SRV used these for a while. They are 40W amps that had these 15" speakers in them depending on the year Fender used different speakers. JBL D-130, Jensen C15N, or CTS 15" ceramic. This is/was an awesom sounding amp. Listen to SRV soul to soul and you will hear vibroverbs all over that record.