As seen in the following image the sparks are really slow to simulate:

https://i.imgur.com/s9SIh69.png

From looking a bit at the code there's 3 issues:

• Way too much state in the data watcher, the client shouldn't need to know about any of this.
• Constant de-serialization followed by serialization instead of keeping the data in field and using the world save.
• Apparently they are stationary, so they shouldn't be entities at all. There's more efficient layering techniques than using entities.