$15K to match Delta would not be acceptable to me unless the eligible spend also matched Delta. For example the United credit card spend waiver does not apply to 1K but Delta credit card spend counts towards Medallion. Similarly, "Economy Comfort and Preferred Seats purchases made through a Delta channel (including delta.com, Fly Delta mobile app, Delta Reservations, Delta kiosks, and select Delta airport locations) are included in MQDs" while United does not count that spend.