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.

The software in modern engines wouldn’t let you do that anyway. The engine startup process can be quite long - several minutes in a 737 MAX - while the engine’s ECU brings things to proper temperatures etc.

But with e-taxi, the startup cycle could be performed while taxiing, potentially saving airlines time on pushback as well as fuel/maintenance cost savings.