so much babble, sorry. The exercise of the right of first refusal was nowhere mentioned by the OP.
Now get to the point: if the municipality wanted the money, how much would it be? And would you still want to buy the house or would the seller want to sell? if yes, consider how you want to
a) deal with money for the municipality
b) deal without money for the municipality
and have that included as an option in the contract.
If no, then have the notary contract drawn up on the condition that the municipality wants nothing.
Whether they want something can only be told to you by the municipal council but certainly no one here in the forum.
The exact amount would have to be determined by an appraisal committee. The difference between the purchase price of the land in 2015 and today’s value would be about 90,000 euros.
To be honest, the likelihood that the municipality will assert its right of first refusal is not a concern; I have been told the probability is very low. Since the property is in a new development area, I have no worries about that.
Would we still buy the house if the seller had to pay 90,000€? Yes, of course, but the seller would have to have the financial means.
Splitting this amount would be an option, but it’s “not our problem,” so it would need to be negotiated precisely how the shares would be divided.
After many answers for which I am grateful, I have to admit that you are right... We will only get the answer from the municipality...
Thank you very much!