20 GB JSON is surprising to me. I have an sqlite file of all HN data that is 20 GB, it would be much larger as JSON.
$ du -c ~/feepsearch-prod/datasource/hacker-news/data/dump/*.jsonl | tail -n1
19428360 total
Not sure how your sqlite file is structured but my intuition is that the sizes being roughly the same sounds plausible: JSON has a lot of overhead from redundant structure and ASCII-formatted values; but sqlite has indexes, btrees, ptrmaps, overflow pages, freelists, and so on.