No it won't. The ratio of minerals to CG or alloys is the exact same.
So let's make it simple. If one mineral = 1 alloy, as is the conversion in game, and one mineral = 1 CG. Now let's say you have 2 minerals. If you take a +15% increase in alloys and a -25% in CG, you now have 1.9 minerals, because your first mineral is 1.15 and your second mineral is now .75. Add that up and you have only 1.9. So you've actually lost minerals.
If you were to just replace a CG factory with an Alloy factory, you'd still have your 2 minerals. The differential math makes it impossible to come out on top if you choose anything other than balanced. If it were -15% and +15% you'd have a stronger reason to take something over balanced.