In my opinion, comparing two XS15's to one PB12-Plus would make more fiscal and logical sense.
2ea, XS15's...... = $1,423.00.
1ea, PB12-Plus = $1,399.00.
The beauty of two XS15's, you can stack them (conjoined) or you can dice them and set them in separate locations about a room. Can't do that with a single PB12-Plus.
At this price, why not compare a XV30 or a XV30f with the PB12-Plus? All three are $1,399.00. Now we're comparing chocolate, glazed or plain doughnuts from the same shelf. Doughnuts are good. With a cup of black coffee, yum!