That ideology is way out of date in thinking captive fish grow to smaller sizes than wild fish. The fact is, with advances in diet, filtration, and maintenance, that captive fish actually can grow larger than wild fish.
What was causing "stunting" earlier in the fish hobby was poor water quality. A condition known simply as brown blood disease (nitrite poisoning) causes a form of stunting through lowering the blood's ability to absorb oxygen. This condition inevitably lowers the fish's immune system and life span which yielded a visual result of attaining a smaller adult size and lethargic behaviors.
Nowadays, a multitude of species are reaching sizes far greater than their reported wild sizes. Just look at the large species being maintained in Asia, Europe, and more and more in the US. As the science of the hobby expands, our fish are living better, healthier, more long-lived lives and one of the payoffs to these advancements is watching them hit larger sizes.
Now, to answer your question...under proper conditions, yellow perch can attain a size of 15 inches. That size is attained by species living in states where ponds/lakes freeze over and in southern states that don't experience freezing temperatures.