Theres a few things I would try.

Make sure that you dont have too many files are running in preview, too many files with preview enabled can slow down the loading process.

You can also use .constant() to supply static data so your program doesnt have to fetch or process real data.

Xcode can accumulate a lot of derived data over time, which can sometimes slow down builds. Go to Xcode > Preferences > Locations, and click the arrow to open the Derived Data folder and delete it manually.