It won't be a 12k seater stadium, last week it was 15k, when it first came out that SISU were planning to build a stadium it was 25k, next week it'll be 8k, stop lowering the attendance to suit your argument.
I don't think a stadium would be built with a capacity lower than Highfield road, that would be pointless, if this ground was built, it would have to take into account that in the 3 years it will supposedly take to build we should get promoted by then, therefore a 15k stadium would be too small, again, success in L1 would get 15k+, we got 15k v Shrewsbury and we weren't even in the playoffs at that point.
Think about it, the ground would have to be at a minimum 20k to satisfy demand or even potential demand.