As long as you achieve significant energy savings by replacing the windows in an old building, the effort is worth it. Windows have different properties. Pre-1995 models often have poor thermal insulation. If necessary, contact an energy consultant, who will determine the thermal insulation value (U-value) of your windows for you.
If your U-value is above two, it is worth replacing the windows in your old building. New windows will significantly improve the insulation. You will normally save several hundred euro annually.
If you are in the process of optimizing the energy efficiency of the building, spare a thought for the doors as well. Replacing the entrance door in your old building will also help optimize thermal insulation.