Rasa NLU model to old
I believe you trained this model on the previous version of Rasa NLU and updated Rasa NLU to a new version (Rasa NLU is a dependency for Rasa Core, so changes were made in requirenments.txt file).
If this is a case, there are 2 ways to fix it:

Recommended solution. If you have data and parameters, train your NLU model again using current dependencies (this one that you have running now). So you have a new model which is compatible with your current version of Rasa
If you don't have a data or can not retrain a model for some reason, then downgrade Rasa NLU to version 0.14.6. I'm not sure if your current Rasa core is compatible with NLU 0.14.6, so you might also need to downgrade Rasa core if you see errors.

Good luck!
I have a problem. I am trying to use my model with Rasa core, but it gives me this error:

rasa_nlu.model.UnsupportedModelError: The model version is to old to
  be loaded by this Rasa NLU instance. Either retrain the model, or run
  withan older version. Model version: 0.14.6 Instance version: 0.15.1

Does someone know which version I need to use then and how I can install that version?