Simulink model initialization time is huge

I'm trying to run a simulink model of an MPC.

All works perfectly at the beginning, but then I decided to increase the simulation time from 15 sec to 20 sec. As I expected, both the initialization of the model and the simulation require more time.

However, when I come back to 15 seconds, it happens that the initialization time required by simulink still remain high, and actually increase! I do not get why (it should reduce, coming back to the initial situation - I mean, the time should be the same of before my change from 15 sec to 20 sec)

There is a way for solving it?