16GB is for cache, not dedup.

No, upgrading to 16GB will not meaningfully improve deduplication performance.

Deduplication on ZFS needs the dedup table (DDT) to live in RAM. With 8GB, you’re already in a bad spot — the DDT for even modest datasets can be gigabytes. Going to 16GB gives you a bit more room, but the table will still spill to disk, and that kills performance. Dedup only works well if you have enough RAM to hold the entire table. For a small home NAS, that usually means 64GB or more.

What 16GB will do is improve caching. The ARC (Adaptive Replacement Cache) gets more space,