Last time I looked there was no way to really tune or limit RAM use, if their github is anything to go by. The only thing I really noticed was that you could limit the index size, and the maximum memory to use when indexing.
Results on my instance are returned by time, by default. You can adjust this with the rankingRules, as per their documentation.
In my experience it is on average quicker to return results with popular topics loading in under a second. Most other searches feel nearly immediate.
I installed both side by side and disabled elasticsearch when I wanted to test meilisearch. It fit my needs so much better that I never turned es back on. I think that if you have a need to tune/limit RAM use, es might still be the better option.