Battery packs are usually marketed with their capacity in milliamp-hours. I thought the 15-20k mAh made it pretty clear that we were taking about a 15000-20000 mAh battery pack.
Insisting on changing 15k mAh to 15 Ah is the same as insisting on changing 15000 mAh to 15 Ah - which seems to be a matter of personal preference more than anything.