Slow test file compilation in Swift 1.2, Xcode 6.3.1

I experienced much slower compilation of the swift unit test files after migrating the project from Xcode 6.2 to 6.3.1.

My unit test use Quick/Nimble framework. Also in each test file I have:

import MyApp

The interesting thing is that when I comment out that import, the compilation is lightning fast. I tested it out on some dummy unit test files, that in fact don't use any of my application's code. But that import makes huge difference for the compilation time.

I didn't observe that big impact when using Xcode 6 - 6.2. Do you have any ideas how to improve the compilation speed now?