I'm not sure that DS-15 is so long lived. In this text that I copied from his web site before it disappeared, he seems to be saying that DS-14 is a better keeper, given that it's suitable for the Nova which most people don't like emptying and refilling too often:
Originally Posted by Gerald C Koch
DS-14 is an excellent standard print developer. It is a modern formulation using safer alternatives to hydroquinone, and it performs like classic standard print developers. This developer is recommended for users who use Kodak Dektol, Kodak D-72, AGFA Neutol Plus (discontinued), Ilford Multigrade Developer, and other standard print developers.
DS-14 is suitable for processing in tray, tank and Nova slot processors, and standard developing time is 1.5 to 2 minutes. DS-14 can be replenished by top-off method. Use DS-14 itself, minus potassium bromide, as the replenisher. If colder tone is desired, 0.05g to 0.3g benzotriazole can be
added to DS-14.
DS-15 is suitable for tray processing, and processing time varies with paper stock. The bromide in DS-15 can be increased or decreased for desired result.
I mix Ilford ID-78 for use in my Nova and it seems to last well.