it sounds like you may have dimensions/constraints on your levels that are locked somewhere.
If you cannot find where they are locked, you can do this:
in an elevation or section view, draw new dimensions between your levels. If you see the little "closed" padlock next to the dimension, they have, indeed, been locked. You can unlock the dimensions and make changes to your level.
Warning: if you're copy/monitoring correctly, you will get a "Coordination Review" message if the arch model hasn't been updated to the 150mm change. Typically, it can be ignored (meaning you can continue to work without it fouling up your project) but it should be communicated to the Arch if they need to adjust their level, also.
