Upgrading XCode to 9.1 and iOS Simulator to iOS 11.1 has slowing down Appium-java based tests drastically.
My set-up
Previously it was as below & tests were running with speed
The issue has got resolved using latest version XCode 10, Simulators on latest iOS version 11.4 and using latest Appium runtime 1.8.2-beta from npm. Need to the fresh install of iOS to 11.4 & remove any 11.3 / 11.0 / 10.3 version.