Is your feature request related to a problem? Please describe.
There's no config option to control Rubber Tree generation in Fabric version of the mod (1.15.2)

Describe the solution you'd like
The one present in 1.12.2 version of the mod.

Here it is, for reference (from ores.json)

"rubberTreeConfig": {
    "shouldSpawn": true,
    "chance": 75,
    "clusterSize": 7,
    "sapRarity": 10,
    "spireHeight": 4,
    "treeBaseHeight": 5,
    "rubberTreeBiomeBlacklist": []
  }