This part might take longer than 15 minutes. It could possibly be done quickly, but without having intimate knowledge of how their system handles data from the keyboard, I can't say for sure.
On the other hand, if they were clever, they could write a subroutine to let the operating system do all the work for them without the need for an external computer.
It's not like they have anything better for the processor on the phone to do, right?
A nice standalone program like that would make a great app to run on any unlocked phone. There's nothing stopping anyone from building the app given that code running in RAM since only the OS loader is signed by Apple.
You claim in your other answer that is precluded by the offer to Apple to run in their own space. It doesn't really matter what is in this offer. The next offer might not be so generous, or the offer after that. Drawing the line here makes lots of sense. There is no way the tester is anything other than a back door which will be requested by everyone.