The song has two different sets of lyrics, one in Swedish and one in English, that are rather different. Both versions are written from a first person perspective as if the king himself was speaking. In general the lyrics are mostly poetic in style and contain fairly little factual information that can actually be checked. In places they do make references to well documented historical events, but often in an indirect manner that make it difficult to discern the underlying event if you are not familiar at all with his reign. The "waited 15 years" part is a reference to the fact that he was crowned king at age 15, after a short period of Sweden being ruled by a rather weak council. His crowning ceremony was also rather unusual in that he, unlike all other Swedish kings after 1594, did not make a "konungaförsäkran" which is a form of oath of office, and placed the crown on his own head, rather than having it placed there by the Archbishop. The Archbishop was, however, present at the ceremony, an participated in the other rites that are part of the coronation ceremony. These events seem to be alluded to in the lyrics but in such an indirect way that it might be quite difficult to understand what they actually refer to - it's more poetry than a verifiable account of events. Still, Sabaton did have the lyrics fact checked by a biographer of Karl XII, as he is known in Sweden. If you are curious about him I'd probably recommend finding a biography about this dynamic but also controversial king, rather than trying to determine the historical accuracy of the of the lyrics. Edit: spelling