Heh! That is funny!
In every picture I find online of one of these receivers it is printed saying 12DC... and I too saw the same in the manual as well as any online spec lists.
I'm still going to go with that it will be perfectly fine to power as I suggested above.
I know that if it really does need 15V no harm will come from giving it 12V, so at the very least, you can feel free to test it out for us
I'd bet that the difference would be a very slight change in the available headroom. Likely so slight that no human ear could perceive it, but might be able to be measured with a fairly expensive Audio Analyzer.
Plug it in and rock out, then let us know what you find!