There is this world, and several people came out of a cave without any memories, but they do have basic knowledge of survival. Years later, the descendants of these people are fairly progressive and have made beautiful architecture, and are at about the technology level of Lord of The Rings, without the magic. They are progressive and pursue change.
My question is how long this civilization could theoretically go without inventing new technology to launch the civilization into a Renaissance, also without actively avoiding it. I know that other questions on this site have covered how long technology would take, but my question is different because this covers a different technology level, and they aren't given any advantage.