There are a lot of topics on optimization in this forum and in the docs:
- Question (or a lot of questions) about performance and optimisations
- Optimizing the scene for a huge amount of simple meshes
- Optimization : Freeze active meshes, Merging, Instances
- Optimization - merge instances
- My experience in Babylon performance optimization and problems encountered
- Optimize your scene - Babylon.js Documentation
- etc
Lately, thin instances have been added to support even faster instancing (docs will be available in https://doc.babylonjs.com/how_to/how_to_use_thininstances when validated).