You have been working in the same company for the last 15 years. Your designation as well as boss also remained same. Therefore, your mind was so much conditioned to particular environment that you are unable to align mentally with the new conditions. Rolling stone gathers no moss goes the adage. Your challenge is how to remove the moss on your career's stone that has been gathering for the last 18 years.
One has to face challenges of this kind when one does not do career planning. Alike companies, one has to identify the risks associated with one's career. Long stay in the same company and that too tying one's career to the apron strings of CFO was risky. The risk has become reality now.
To manage the change, you have specified two options. One is dealing with "Land and Property matters". It means dealing with government functionaries. It requires certain skill set. Do you have it in you? But trust me, one you master this job, nobody will remove you from this post. One has to know the inside affairs of the government departments. Secondly, some wheeling and dealing is required. But then has your company given this job because do they consider you as their trusted employee? Why not to take feedback from the employee who left this job and be prepared?
If you take up this job, over a period of time you may move into Admin or Commercial department. One must grow in one's career. If you look around you will find that one time mechanics are running workshops and one time dish washers work as chef in the hotel. Talk to them and you will find them aspiring for further growth!
There is one more reason why you should grow. As of now you could be fulfilling requirement of providing bread and butter to your family but then will your children accept their father's life who preferred very steady career and remained in the same designation for the decades? When your children grow up and by chance question you for not growing in the career, then what reply to give, please be ready for that.
The second option is joining new company with same designation. It is something like resetting a pin of a gramophone disc which was stuck at some point. Resetting pin will help you in listening the same type music which you have been listening for the last 15 years. Possibly you may listen different songs.
It is very difficult for an outsider like us to suggest right choice. You have to decide on it. Nevertheless, at least now please make a career plan and decide yourself with what designation you would like to retire. Whether it is Executive Assistant or something else the choice is yours.
All the best!