I specifically sought out 2015-16 siennas that were of limited or limited premium package vintage.Price aside and if all options/trim same-
Would you feel more comfortable buying a 2019 Sienna with 30k mileage or a 2015 with 40k?
Newer with higher average miles per year vs older with lower.
The main reasons was for the 2015 revision with more body welds and sound deadening material and overall better layout of the dash. pre-2017 so I have the port injection engine instead of the direct injection, and finally those amazing 2nd row reclining seats for our 1200 mile road trips to Florida each year.
So in my case, I would take the older van. The mileage difference is negligible while the newer engine is going to have issues with the DI (valve and intake deposits)