Tyre would be forgotten for a period of 70 years. It is uncertain if this means a literal number of years. It is possible that 70 merely indicates a long time, with 70 being used idiomatically to indicate the fullness of time.
The days of one king
sounds like the reigning period of a king, but 70 years is an extraordinarily long time for one king to reign. It may also indicate the average lifespan of man.
15 In that day Tyre will be forgotten for seventy years, like the days of one king. At the end of seventy years, it will happen to Tyre as in the song of the prostitute: