Why does the interpreted MATLAB function slow down simulink so much and how can I speed it up?

I have built a model in simulink that takes about 30 seconds to simulate ~600 seconds, which is good considering the number of ODE's in the model. However, I am now at a point where I need to include an additional piece of code that cannot be constructed in simulink. For this, I used the interpreted MATLAB function block. When I run the piece of code independent of simulink (as in, I just call it from the command window as you normally would), it takes <0.5 seconds to run. However, when I throw it into the interpreted MATLAB function block, it takes 15 minutes for it to run just 1 iteration of the MATLAB function. This is obviously too long considering how much time I am trying to simulate. What is the reason for this dramatic increase and how can I make it faster?

Thank you!

[Jan]

Without seeing any line of the code, it is impossible to guess the reason correctly. Post your code here and some typical example data.