You are accurately perusing the owner's handbook.
In temperate areas, Toyota recommends the use of higher viscosity oil. The United States presents a complex market due to its high temperature variations, allowing residents to often transition between different climatic conditions. The commercial motivation to get the best possible mpg figures results in the usage of thinner oil in the US, compared to other markets where lifespan is prioritized, particularly in consistently hot regions.
15W-40 is suitable for your circumstances.