It may be face punch worthy for me to suggest this, but I would still keep the corolla.
Unless you have major financial issues, it is a nicer car, should last longer and I honestly think you guys like it more.
If you keep it for its usable life, you wont remember what a fiesta looks like by the time the corolla dies.
Final verdict, at 15K a year, sell the fiesta and enjoy the nicer corolla. You will get your moneys worth from it.