I thought I'd seen the paragraph in the tech section - directly addressing your question.

What's Better? A14 or A15?
It depends on what you mean by 'better':

* A14 often have better availability, meaning you can find one at an inexpensive price.
* A15 has 7% more capacity than the A14, meaning an automatic power increase in low and mid-range RPMs, all else being equal
* A14 and A15 stock bottom ends can both rev to 8,500 rpm so there's no advantage there.
* Since both use the same cylinder head, there is little top-end power advantage with either engine

So there you go!

Edit: heres the tech section link http://datsun1200.com/modules/nsections/index.php?op=viewarticle&artid=26