Performance could (and should) be better than this of course, mainly when it comes to the gpu side. I would call this well optimised myself if the gpu side was 1.5-2x faster.
The goal of this demo is mainly to show that making something somewhat nice looking is possible. It is here to show potential, what if a studio with actual budget and people would work on something? (And not just one guy in his spare time, who does not even have any gamedev or even IT education.)
Anyways, I hope you liked the demo, even with its flaws.