Have I missed the post where you have attached your model so we can check it for any possible strangeness on our systems.
Sorry for the late reply, ended up using the cloth system of a different app to get my result. But there is no model to attach, as it is simply an issue with every one of my models. But I have simply found an alternative instead of a fix, unfortunately.
The other day someone else reported extremely slow behavior in Clothworks. It turned out they had Gravity set to 0 instead of 9.8 which would be normal.
I expect then it has to do with either your setup for the extension or your hardware. Sharing one of your model files would help sort out where the problem is.