DbContext is very slow when adding and deleting

Try to add this to your DbContext tests:

dbContext.Configuration.AutoDetectChangesEnabled = false;

// Now do all your changes

dbContext.ChangeTracker.DetectChanges();
dbContext.SaveChanges();

and try to run your tests again.

There was some architectural change in DbContext API which checks changes in entities every time you Add, Attach or Delete anything from the context. In ObjectContext API this detection run only when you triggered SaveChanges. It is better solution for most common scenarios but it requires special handling for mass data processing.