I took a look and have a few tips:
- You may already know this, but if not: you can enable the 'display timing' option to see how long each individual node took to compute. There will be some variation in timing each time a node is updated, but it gives a ballpark estimate of performance.

- The "shape splatter" node is somewhat performance heavy. Try not to use it too much. Sometimes a 'tile generator' and a blend node can give comparable but faster results. Also, 1 shape splatter with 6 inputs is faster than 2 shape splatters with 3 inputs.
- Most "grunge map" nodes are quite performance heavy. Try re-using the same grunge map node or use cheaper alternatives (most of the other noise nodes are quite fast)
-- The 'Twig' node also contains a few grunge maps. Each time a twig node is used, all of these grunges are generated again.
- The difference in performance between 8-bit and 16-bit isn't that big. I actually recommend keeping most, if not all parts of your heightmap in 16-bit to prevent banding and pixilation issues.
- Lowering resolution for some nodes
is a very good way of improving performance. I noticed you're already doing this, so that's good.
All in all I honestly don't think the performance of this material is particularly terrible btw. A material with many elements like twigs, rocks, puddles etc. will always be a bit slower than a generic brick material for instance.