It doesn't really matter what you start with. Both platforms are comparatively equal.

The A15 would already have a H89 cylinder head on it. The A14 may only have a H75 head which is a dry manifold type meaning it does not allow coolant through to the manifold.

If you get your setup up and running I would say you would have the first operational EGI setup that has come to life in the recent decade. Lots of people buy and sell and they generally move around the country but few people take it on and complete it. I'm wishing you all the best. My project also stalled as I couldn't source an original ECU.