What? I've had 16k maps before (A 19) and they play the same as an 8k, just bigger. That was on my old computer. I've since upgraded so I have no problems playing any game now, including VR. In fact, I have a 16k map and if I could get the biomes.png right I'd be playing it. The game does not load the entire map all at once, just a selected area that is in your view. So it does not matter the map size, the amount of information being processed is the same. So a larger map does not use any more resources than a small map.
I've been playing this game since A 16 and until the A 19.5 update, you could make 16k maps with NitroGen. I played them all the time in SP and multiplayer. 8-12k maps are just too small.