sometimes when you are running a very large size airline, or you didn't manage to hope on one of those popular next generation replacement because you took one too many at the bar the night before, you are stuck with an aircraft that you will have to use a little bit longer then you wanted. At 16 years unless it is a very popular aircraft such as a330... I would advise skip the check and scrap it before hand.
Since you are talking about leasing out or scrap, you own the aircraft. so it's not that terrible to use it for a little bit longer. and scrapping is best option overall.(assume you DP your aircraft from the beginning, you already saved a ton of cash).