Aint that the truth!
You may be aware that Ampeg did in fact offer the 115 cab with an optional Altec 418-8H Series II driver in the seventies.
Luckily I still have a pair in the studio.
Not for the lightweight boys this thing, it was rated at 150 watts had a Huge Alloy Frame and a magnet big enough to influence the path of passing comets.
One is as loud to the ear at moderate volume, in parallel with my Eden 8 X 10 LXT cab also 8 ohm.
So it must be very Efficient

!, for one fifteen to be as loud?!
It has a fantastic tone and responds really fast with a tingling brightness and upper mid openness the eden hasn't, Its got no tweeter just an alloy dome center cap.
Well Bill F,M will say it has no response off axis, thats true!, but my mic don't know that cos it isn't off axis.
Maybe it wont trigger seismic shifts in the earths tectonic plates but it sounds full and fat on a b.
The thing is it records very well indeed, no it doesn't sound retro it just sounds really really good.
The old CTS Alnico 15's in the oldest flip Tops are a similar tone over power lightweight cone and voice coil type.
New Ampeg 115E's are just dull and thumpy in comparison.

Bring back lower powered wide frequency response, not just all the design in power handling and dropping the fundamental resonance to 30 HZ and all that ICE influenced bollocks, can I have 15" midrange tone so the records I make can play on a I pod and you can still hear the bass well?. Well its seems only with the very old stuff you can, without it sounding like honking geese or some mad tuba that is.