I own a Ref 110 and it is much better than the VS 115. I have not heard the new Ref 150 so I can't comment on it. So far my dealer does not have a demo. I would like to hear one but have no plans of replacing my Ref 110 in the near future. I do plan on using kt120 tubes on my next retube. I would also like to compare a Ref 110 using the kt120 tubes with the Ref 150.
It will probably be a while before you can find a used Ref 150 at a reasonable price.