As long as you have 2-3 paid international business-class airfares then you should be OK, but anyone who doesn't travel internationally in paid international business-class will find it difficult to spend $15,000 unless they can afford paid domestic first-class tickets.
Besides being absurd, there is absolutely no reason why anyone who can spend $250,000 on a credit card should be using a Delta-branded American Express that only gives 1 point per $1 of general spending. There are much, much better credit cards out there.