It's not really hard to complete. Yeah, it's annoying to build on small islands, but the required prosperity is very low. The scenario is technically beatable with large hovels, but I went for small casas because there's no reason not to and education buildings are needed to reach the culture goal anyway.
Here's a screenshot of only the used part of the map (only a quarter-ish): https://imgur.com/a/sWSDOOr
Final ratings: 75/35/100/100 with 6511 people all living in small casas.
It would be more of a challenge if fishing wasn't allowed and/or if one needed to have patricians or at least insulae, because then you'd need to provide the houses with consumable goods.