Can a zero-drop shoe have a 15mm stack?

Yes. Drop measures the height difference between heel and forefoot; stack describes the thickness between foot and ground. Notace lists both zero drop and a 15mm stack for Michi 1 and Yama T1, while Koto 1 has zero drop and a 19mm stack. Zero drop does not mean no midsole, no cushioning or an ultra-thin sole. Compare midsole material, outsole construction, fit and activity alongside the drop measurement.