True, the engines need to be warmed up and the hydraulics need to be pressurised, but given e.g. airbus recommends single engine taxi without APU (SETWA) warming up the engines probably doesn't take that long in the grand scheme of things. Definitely not the 15~25mn of taxi. From the sources I can find, "normal" warmup takes 2~5mn depending how long ago the engine was shut down, unless outside temps are exceptionally low, and you can do that while reaching the end of your taxi.