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Boost is a way of increasing the displacement of an engine with out increasing the size of the pistons or bore and stroke of an engine.
If you run 15 PSI boost, in effect the engine size is more then doubled, and in theory horse power is doubled.
So with lower boost, you get less power, but better fuel economy.
Higher boost yields more power and less fuel economy.
As boost increases, so does inlet air temperature. There is a point at which this temperature becomes high enough to ignite the mixture before it evens enters the cylinder. So higher boost requires more cooling of the inlet air. Because of the tendency for pre-ingition, there is also more advance put into the ignition curve. Also valves tend to float at upper limits, so new valve springs and retainers are in order.
No not all engines require special pistons for high boost. But it is a roll of the dice as to how well a factory engine can handle the extra pressure. While factory pistons and crank shafts may work, there is too wide of a tolerance allowed at the factory. Things like deck height, balance tolerances and manufacturing defects.
So a higher boost engine needs a greater attention to detail. As a matter of fact, any engine that is to be pushed to the max needs this. So a custom (for want of a better term) rebuild is in order.
This is in no way a complete answer, as there are a lot of engines out there, and each manufacture has just too many engines to completely generalize.
Take the four cylinder engines, for some makers you had better plan on a new block on out or at least on tossing a few before you find one that will take the boost. While others just need to have the engine balanced and new bolts installed. Because you are asking this question in the Mazda section, I would suspect that your planed application will not need a whole lot, just a rebuild that pays attention to detail.