Bison, I do not think it is possible to give a quantitative answer.
First, are we talking about scenes in terms of location changes, or just changes in the combination of people in the same location?
If scenes involve location changes (and therefore set changes), then the number has to be fairly small.
But some scenes are not location changes. In other words, persons A, B, and C can have a long scene in an office, and then A and B leave. At that point D and E come into the office and have a long interaction with C. There you have what you would have to consider two scenes, though they are continuous in the same location. If you have scenes like those, you can have a lot of scenes in a three-act play.
The best answer is just to keep the number of set changes small. After that, the story will determine the number of scenes.
The number of reasonable scenes also depends on how the scenes will be handled. Bare-bones productions with few props can accommodate more scenes than productions with lavish sets.
Ray