My team and I have experienced very slow performance from XD while designing for the past few weeks. It often takes several seconds (anywhere from 5-30 seconds) after clicking on an element for it to actually become selected, and then it takes even longer to move an object. Zooming in and out is also very slow. We tried unnesting components in the design system file we link to, but the performance didn't change. This is an issue with all of the files we've worked in, and we're on Windows.
We're so sorry to hear about the trouble, we'll try our best to help you with it. I'd request if you can share a few more details like:
Thanks for sharing the details. Please update XD to the latest version that is 18.104.22.168 and let us know if its better. If it is still slow, we will need to isolate the cause of the slow performance so could you please try booting the system into Safe Mode (https://support.microsoft.com/en-in/help/12376/windows-10-start-your-pc-in-safe-mode) and check how it works there.
It is still slow and having the same problems.