A partial release clause is the mechanism that lets a subdivided parcel actually be sold in pieces while one loan sits over the whole thing. When the plat records, the lender's mortgage still blankets every new lot. A buyer of lot 3 can't get clean title until the lender signs a release for lot 3 specifically. The clause sets the price of that signature in advance.
The 115% isn't an extra fee. Round numbers: $600,000 loan across 12 lots is $50,000 pro rata per lot, and 115% of that is $57,500 of sale proceeds going to the lender for each release. Ten releases put $575,000 against the loan and the eleventh clears the last $25,000, so the mortgage is satisfied with a lot or two still unsold. The lender never collects $690,000, because release prices stop when the note is paid. That's the whole point: principal comes down faster than the collateral does, and the final lots close free and clear, subject to accrued interest and any release fees. That's the whole point. The lender is paying itself down faster than the collateral shrinks, so the loan gets safer with every sale rather than riskier.
The minimum unsold lot requirement does the same job from the other end. If you sold the four easy lots first and left the lender holding the wet one at the back with no road frontage, the remaining collateral wouldn't cover the remaining balance. Requiring three unsold lots keeps a cushion in place.
The number worth checking in any deal like this is which lots the release prices apply to. Some sheets set a flat per lot release, which ends up punishing you if your best lots sell first and your cheap ones last. Others set lot-specific releases off an appraiser's lot values. Ask the lender to show you the release schedule lot by lot, in writing, before you sign anything, because that schedule decides whether you see any cash before the loan is gone.
