I think you and a lot of other people. And most people buy without diving into the technical specs like we do here. Everything else roughly equal (price, performance), people will choose a bigger sounding engine.This exactly. If they put a 1.5 liter turbo in there I will not be getting the Civic Si. I'll go with the Focus ST or even the 2015 Civic Si.
I'm surprised you'd choose the 2015 Civic Si over a 1.5T Si though. The driving dynamics are already reviewed to be a ton better in the 2016 standard models and the Si's engine performance (even if just a 1.5T) is guaranteed to be better than the current Si.