AFAIK, a lot of the RAM requirements come from importing and processing the data. It already takes quite a long time and would be even slower without heavily utilizing RAM.

Nominatim also doesn't support any sort of typeahead queries. There's Photon(https://github.com/komoot/photon), which works in concert with Nominatim and is similarly tied to OSM as a data source.

There's also Pelias(https://pelias.io/), an open-source geocoder that handles all types of geocoding in one and supports OSM, OpenAddresses and many other sources (including custom data) out of the box. Admittedly it can have more moving parts as a result, but it can be set up with relatively little RAM if you're careful (I bet a planet install could be done somewhat slowly with 32GB RAM). Full disclosure, I have been a core-maintiner of the project since 2015.