"TDD is slow because you're writing twice as much code"
Okay, let's pick this apart.
First of all, how much of our time is actually spent writing code? It's typically a lot less than devs think.
Secondly, how much of our time do we spend debugging code? It's typically a lot more than devs think.
Thirdly, would it be less time writing code if we wrote the tests after? Can't see how that follows.
So, it's not TDD, is it? It's writing automated tests you have the problem with.