This is where the old speaker properties are not determined by speaker diameter thing comes in.
4 10s will have more speaker area so might have more sensitivity, but this could be offset by being in a sealed box. A 15 in the same size box as the 10s with will have more breathing room, so possibly better sensitivity in the lows, plus 15s are generally in ported cabs, also adding sensitivity in the lows. Really, there are so many other possible factors, it all becomes a bit irrelevant to generalise.
Basically, anyone who makes a statement about speaker size/number affecting the properties of a cab, outside of other considerations, is wrong.