Xcode 10 runs really slow and slows my entire computer down
I do have the same issue - unlike many other posts on the Web, I only have one view controller with a couple of slides and views, so simplifying is not a solution for me - 

I suspect the simulator seems to slow things down - there is a SimStreamProcessorService which seems to take a lot of CPU time (look at Activity Monitor under %CPU) -

I restarted XCode and didn't use the simulator and it seems to be running fine.  I have a MacBookPro late 2011 with 16GB RAM running Sierra -