I'm not sure what you mean by 150VBR. Many encoders apply apparently meaningless numbers to their VBR settings. If that's what you're talking about, then there's no way to tell at all. VBR settings are not specified by bitrate, but by how accurate the encoder tries to be. Most encoded at the same VBR setting will approach the same bitrate, but could, conceivably, vary wildly in the face of some (as the Perl guys put it) pathological input. Even knowing what bitrate it tends to average out at isn't going to help because you could encode a 96kbps CBR, which would sound pretty bad, but a VBR file that averaged out at 96kbps could sound pretty good, if there were huge sections of easy-to-compress audio in there, or it could sound equally as bad, if it was fairly consistent.

If you are, instead, referring to 150ABR, then that's a different matter. In that case, the encoder tries to get the average bit rate around the specified number. Unfortunately, there's still no way to tell. It should at least be slightly better than a CBR of the same rate (not there's any such thing as 150kbps CBR), but because of the way most try to deal with averaging (few, if any, do a multi-pass encode), it might not be. It's certainly not going to be a lot better, because the encoders are fairly conservative and don't stray much out of the specified bitrate, because they never know when they might need more bits or have some left over.