You can use a 225-50R15, it will fit on a 6.5" wide rim
The 15" fOCUS wheels are 6" though, not 6.5".
That's really pinching a 225 on a 6" rim, and more often than not will result in reduced performance.
The contact patch may end up convex instead of flat due to the sidewalls being pulled in so much.
I'd take focusedaddiction's suggestion and find yourself some 205/50s.
Or, maybe a 215/XX, though I'm not sure if there's many to choose from in a 15" size.