No way it will be 15%. A drop of half is generous...I honestly think it'll be even worse than half. If they offered a Latin alpha child set, your 15% variance might be correct, but with no Latin alphas even as an add on kit, half is the minimum drop I'd expect, if not worse.
You guys' prediction are so strange. How many people do you think are feeling "slapped in the face" because of the change? On Massdrop of all places, tons of the purchases come in from people who have absolutely no idea the set even exists at this current moment; the vast majority, really. I think a projection of 20% is actually generous all things considered.
You're blowing this out of proportion because you want to support your side of the arguments' bias. I don't mean this in a demeaning way, it happens all the time and everyone is susceptible to it but it really doesn't matter. This isn't Zambumon's first time designing a set, no one wants its success more than he does - if he thinks this is the right move, it absolutely and factually is the right move. If he wants to risk sacrificing his royalties and/or recognition by making a stylistic choice of this kind that's on him.
You have to understand that whilst your opinion is valid and entirely relevant, in the grand scheme of things your 2 kits purchased (or not) are a drop in the bucket. It's like when ICs are filled with people begging (more like demanding, usually) NORDE ISO support and then the set goes live and the same people that complained are now saying the price is too high and they don't buy anything anyway and the kit ends up with 20 units sold and having to be rescued by Massdrop's good relationship with GMK/SP.
The set will do well regardless and neither party will be proven right/wrong.