With Tableau 2018.2 there is a improved caching and parallel execution to provide better performance in MDX queries,
Is there any more documentation available that explains this a little more in detail than just a headline?
At my customers we run SSAS and have not seen any improvement, perhaps there's a setting we've missed?
I am going to reach out to the Tableau Development team to see if we can provide some more details on the improvements.
Thanks for posting!