It is a stylistic decision, but there are occasional cases where repeating yourself may be advantageous.
If you have "three to four billion dollars" omitting "billion" after "three", it's potentially ambiguous as to whether the lower bound is three (3) or three billion (3,000,000,000).
Generally in the real world there is little ambiguity, especially where one number is more than a billion times the other. In the first sentence, the difference is less, but a salary of fifteen dollars a season would be improbable, so the "thousand" after "fifteen" is likewise unnecessary.
But there are cases with a wide range of values where there may be genuine confusion. (Newly created example: "Prices of paintings range from ten to fifteen thousand dollars". It's possible to pay 10 or 10000 for a painting.)
It does no harm to repeat yourself, and some newspapers may prefer to avoid ambiguity as much as possible, even if it's probably unnecessary. On the other hand, some people may prefer to keep it short.