Why "Initializing" step during code generation from Simulink model takes so long?

There is a big Simulink model. Due to the fact that I am not able to make External Mode running in referenced models, I have merged the referenced models into one big top model. During code generation there is a step "Initializing" that takes very long. For example, the whole compilation and building takes 1 min, while Initialization takes 2 min. Why does it take so long? Is it possible to reduce this time (I am interested in code generation only)?

If this is not possible, I would be grateful for looking at my other question:

Is it possible to autmaticly switch between referenced model and subsystem in Simulink? - MATLAB Answers - MATLAB Central (mathworks.com)

[Mark McBroom]

Why are you trying to run a referenced model in external mode... why not run the entire model in external model.

You can use the sldiagnostics function to narrow down the cause of the long initialization time: https://www.mathworks.com/help/simulink/slref/sldiagnostics.html