Everyone is guessing about the mileage here. You cannot give suggestion based on your assumptions.
According to tests done by different auto journalists in the Philippines, Yaris/Vios 1.3 CVT clearly have better mileage than 1.5 CVT.
Here's one example of AutoDeal Philippines. This is what they say about 1.3 CVT
An hour running at an
average speed of 90 km/h returned 22.3 km/L, while spending the same
time in heavy traffic read back 10.2 km/L. Faster paces at around 60
km/h on a Sunday read 14.2 km/L. Take note that these fuel economy
figures were taken with only one occupant inside the car without any
cargo.
Ref: https://www.autodeal.com.ph/articles/car-reviews/2019-toyota-vios-1-3-review
AutoDeal did a detailed review for 1.5 CVT as well and here's what they say about fuel economy
Of course, with a bigger engine, the Vios G was less
frugal than its 1.3L counterparts, but it wasn’t bad at all. An hour of
crawl through city traffic returned 8.1 km/L while doing Sunday errands
at an average speed of 60 km/h clocked in 13.1 km/L. On the highway, I
got a good 19.2 km/L while trying to keep the car at a steady pace at 90
km/h for 30 minutes.
Ref: https://www.autodeal.com.ph/articles/car-reviews/2019-toyota-vios-1-5-review