Simulation models are data intensive. Saving can be slower if you aren't saving to your local device or if there is a lot of unnecessary data being saved with the model.
If you are saving a model over a network or to the cloud (e.g. One Drive), a lot of "handshaking" communication has to occur and that slows the process considerably. If you want to save to some place other than your local device, save to the local device and then copy or move the model to wherever else you want it to be kept.
Look at the data being saved and determine if some of the data can be eliminated. Go to Quick Tips > Memory Management in the ExtendSim Learning Center for more tips on memory management in ExtendSim models.