i create a mesh with 2 lods, drag and
drop it in my level and duplicate it
in the level - that are no instances??
No, each static mesh you drag into your level will be a separate static mesh actor (an actor containing a static mesh component). So that will be two actors.
What I meant with instancing, was to use one instanced static mesh component and only add instances to this component. Then you will have one static mesh and an array of transforms. If you would then want to have 30k lamps you this array of transforms would contain 30k entries. So you would have one actor instead of 30k actors.
If you also want to use lods, then you would use a hierarchical instanced static mesh component.