You have the answer now.
You have zero offset 14x7, wanna go to zero offset 15x8. So you're getting wider by a 1/2" in each direction.
You have 26.5 tall 225 tires now, wanna run 27" tall 255 tires that are an inch and a hair wider section. So, 1/2" wider in each direction
, and a hair taller.
So now, all you have to do is look.
Do you have room for a half inch more both toward the spring and fender, and still have adequate clearance?
If you do...... the combo you described will fit.