For me, I would have 3 possible options: GURPS 4th Edition, Dungeon Crawl Classics, or Edge of the Empire.
It may sound odd to say GURPS due to the system's reputation for crunch, but I've run and played the game enough that I can (and have) run something on the fly if need be. For the players, I could likely guide people through making a character using Delvers to Grow in under an hour. Alternatively, I also have notebooks full of materials made for previous campaigns. Of the three options, this may have the most math, but the system also produces results that generally make sense, so even people new to rpgs could grasp a presented situation (without needing to be versed in gaming tropes).
For DCC, the core book has a pre-made adventure in it that is relatively easy to run without prep. I also have roughly 50 index cards of level 0s ready to go (that I made to get a feel for the system). Level 0 characters are simple to run, so I wouldn't be worried about complexity. If it was for people already familiar with the game, I have other funnels and adventures from which to choose.
For Edge, I own the starter set from when I first started playing the system. It's slightly different from the full set of rules, but it's still a good boxed set. For a group adverse to a lot of counting and adding dice together, it's relatively simple to explain that a player just needs to know whether they got more good symbols or more bad symbols.