A 1.5 tire is in between a lightweight tire and a middleweight tire. I personally would notice a difference from 25 feet away with the big air gap between the fender and tire. The actual tire profile can also vary in size depending on what type of tire, like a knobby mountain bike tire to a street slick. Your rim can take a wider tire just like a car rim. The bike frame and the fenders will dictate how wide you can actually go.
Here's two tires for the 26" S-7 middleweights. 1-3/4".... Big difference between these two tires!
View attachment 1786227
View attachment 1786228
View attachment 1786230