Maybe I’m misunderstanding, but I would try to get a much better understanding of how leases are calculated before going down such a road.
The fact that a 12k lease has a lower payment than a 15k doesn’t mean you got a better deal, only that the bank has a higher RV for 12k vs. 15k; You are paying for less depreciation over the term and thus a lower payment.
Also, the fact that you were able to sell/trade/turn-in your current lease early and be breakeven has little to nothing to do with whether you initially did a 12k or 15k and everything to do with the state of the current used car market.