Re: I've come to the conclusion that the Celestion Vintage 30 is......
Most likely the 15 ohm speakers are not V30's, but original G12H30's if it says it's a 30 watt speaker. AFAIK, the 15 ohm designation was used way back in the 60's and early 70's, and it's been 16 ohms ever since.
The Vintage30 came out in the mid 80's as an ceramic alternative to a G12 alnico. It was designed to mimic the cone response of the 60's Celestion alnicos, but use a less expensive ceramic magnet, and handle way more power.
A lot of confusion is caused by the name, because it's not a version of the 30 watt speakers of old. It only uses the same cone and magnet as the old bass version of the G12H30. The Vintage 30 it's actually a 60 watt speaker, with the same voice coil assembly design as a G12 alnico.