How to properly make a tileset in Top Down?

I have a floor with 37x37 dimensions and I have put actors on every single 1x1 tile of it, like this:

Top view:

3D view:

The reason I did this is because I want every 1x1 tile to be USABLE, specifically build a wall by clicking on it, like this:

79526-walls.png

Only one problem. Lag. Huge. The actors/objects are taking too much memory, so this tells me it’s not the proper way to do it. So I came up with an idea to solve this but I don’t know if it’s possible. My question is, can I make a single big object and then put some kind of pointers on every 1x1 location of it? That way, I can build on top of this big platform instead of having 1370 actors.

PS: If you need to see the blueprint of the actors, here it is: