I'm glad to see more mods like this, betterfps, and fastcraft out and about! However one of the largest sources of lag that to my knowledge no one has addressed is the leaf lag on trees. Jungle biomes, as i'm sure you're aware, is where it's especially noticeable.

I remember discussing it with Allaryin at one point and if I recall correctly he said it had to do with how much and the way they ticked. So I don't know if it's even addressable or not but figured it was worth a mention.

Have you tried using "Fast" graphics?

After looking into the game performance, trees really are not causing a huge impact on FPS. They can sometimes cause a lot of block updates, however this isn't as big of an issue as you may think. 1.13/1.14 basically optimizes trees as much as you can. I did find some info about ticking textures while researching this though, and I think if I can implement that feature successfully it will have a far dramatic impact that this.