You can use vicuna-7b-1.1. No need for chat prompts. Just slam in your data and end it off like so

Generate a JSON with this and that {"this": "

Lower the temperature to minimum for deterministic results, fine tune the other parameters if needed. And have a stop token for JSON closing tag like so }.

That usually works perfectly fine for me in most scenarios. Best: that stuff runs on RTX 3080 with 15token/s (quite fast!). Also vicuna-7b is pretty much as good as gpt-3 when it came out.