Laggy objects (minecraft clone)

So, I’m making a game like minecraft, but at very start i found it to be very laggy because of massive amout of meshes. Looks like this:

I figured out to disable meshes that are surrrounded by all 6 sides, so inside of the world is empty-looking like this:
And my question is what can i do to incrase speed? (like i got 0.5 FPS at 100x100x255 world)
My ideas are to somehow combine Colliders to one big or make visible meshes only visible by fewer faces (only the ones that are visible). Combining all objects to one is excluded because they need to be destroyable by player. Blocks don’t contain any script inside. Everything is done by one script. So what can I do to incrase speed?

did you ever find a solution for this issue?