Computing time of adaptive vs non-adaptive model predictive controller

Hi!

I want to use a model predictive controller and adapt the controller to the changing plant. I created the system and control loop in Simulink and the non adaptive controller works like a charm and easily runs on my real-time system, whereas the adaptive controller takes a dramatically longer time (>10x) to compute. Why does it take so much longer? The calculation of the A, B, C, D matrices is really fast and not a problem... Increasing the step size is not an option and I would like to not change the horzizons (if possible)...

Is there any solution or workaround? I am using Matlab 2017a.

Thank you for your advices and help!

Kind regards

Mark