I think a fair bit of the whole Golden Age shtick is a pure and simple comparison to Jadis. And let's be honest: almost anything would look wonderful in comparison to Jadis's rule. Another part is probably related to Aslan's personal presence at the start of their reign and occasional appearances thereafter. Presumably those tapered off after the Pevensies vanished, though they may not have stopped altogether until around the Telmarine conquest. Thirdly, I think Narnians needed to construct a new national mythos to hold together both those who had suffered through the Long Winter and those who returned to their ancestors' homes after a century of exile and at least partial assimilation in other lands and cultures. The end result is the recasting of the Pevensies as the True King(s) whose ascension ended chaos and in whose reign everything was Good, regardless of the actual facts on the ground.

This is not to say that they were bad rulers -- I think they did the best they could under the circumstances, and clearly by the time of HHB they'd managed to get the southeast (which borders Archenland) into a safe and stable state -- but they were facing a LOT of complications and it's equally clear they fought a LOT of battles over those fifteen years. I mean, apparently they built a navy to rival that of Calormen! You don't spend that kind of money without a very compelling reason.