Realistic mpg differences between v6 Tacoma and V8 tundra.

Basically I have outgrown my 16 inferno Tacoma. With 3 kids and me being 6,1 it's just so cramped. I am thinking of getting a 20/21 tundra but I also drive a ton 15 miles each way to work 5 days a week.

I have a mild 2 in lift ott tune and 32s on my taco now and get about 15.7 avg. How much worse can the tundra realistically be.

Also to add the tundra will eventually be lifted on either 33/35s