reduction of computation time in simulink

In my simulink model I 've made a construction in which a feedback loop with a derivative is implemented, I know I should avoid it, but I have no other choice. The computation time takes almost a day, and I want to reduce it. Making an embedded function for the state variables, could be a solution. I also use a filtering transfer function as derivative (like an observer). But, are there any other solutions in the configuration settings, for example an other solver, other tolerance- or time interval,... , taking into account that I don't want to loose to much accuracy.