2015's are in high demand and Apple knows that. So, they pulled them because they would rather you buy any computer they sell that has USB-C only. Think about it, for every 2015 sold by Apple, that's a 2018 not sold and a step backwards for where Apple wants to go with their line of notebooks. People want the 2015 because of legacy ports and a tried and true keyboard and MagSafe and a glowing logo, etc. And of course, because it's still a great computer. But if there are none available, then folks will be forced to buy something else. Now all of this is speculation on my part, but if I was in charge, that's what I would do to help usher in the new and sweep out the old. Off the record, they probably have a large inventory of 2015's somewhere in some warehouse, but are either writing them off at cost and disposing of them, or passing them off "cheap" to third-party sellers like B&H Photo and other places like that.