Merging meshes with defered decals

Afaik, nope, you cant merge in deferred decals. 9 materials per mesh is pretty bad.
For your purpose, geometry decals are probably more suitable.

Hi,

I have multiple meshes that looks like that

The green boxes are using defered decals. I tried to merge these boxes with the background wall and the yellow grid.
If I do not merge the materials I get a mesh with 9 material slots. How bad is this for the performance? And why it creates so many slots even when the material of the green boxes are the same?

When I merge the materials too it looks like that

Is there a way to merge defered decals too?
If not which is the best way to build “prefabs”? Shall I build my wall with the boxes and then copy&paste the wall for my map? or shall I merge it and use the 9 slotted merged mesh? Or shall I build a blueprint component and use that for the wall? I want to know which way is the best way to not getting performance problems later.

Thank you and sry for bad english.

Ty very much. Can you tell me or show me what these are?