Is the solicitor "your solicitor" or the solicitor recommended by the developer? It sounds odd that a developer can run over on the delivery time, can you runover on when you pay them as well? I would check with an impartial solicitor.
personally dont think a year and a half is a reasonable over-run. I would talk to another solicitor, one with a bit of balls, and get a second opinion.
So the 30 month figure in the contract means nothing. Why put it there in the first place?
It's back to the lack of regulation I guess. In insurance, communications, etc a regulator insists upon the spirit, as well as the letter, of contracts with customers to be rigorously upheld.