One option would be to update the iOS directly on the iPod Touch (if you haven't disabled that option), otherwise you can speed up the process by connecting multiple devices to your Mac at once and update them in one go.
This can be done with multiple USB-Lightning cables plugged directly in to the computer, or by using USB hubs. A more expensive solution would be to buy a dedicated syncing/charging-station. These types of products often allow you to lock multiple iOS devices inside a cage or similar, and have them all easily charge and/or connected to a single Mac for syncing/updating. They come in various sizes for holding for example 4 devices, 16 devices, etc.