Watch for brake clearance if contemplating a smaller diameter rim. If there isn't a half inch between the caliper and the 14'' wheel you may toil. Nor would you would want it so tight that any wheel bearing play allowed the wheel to wrench the caliper off its mounts.
Otherwise, probably the most constraining dimension/clearance will be between the tyre inner sidewall at the top and the MacPherson strut. McStrut slopes inward from bottom to top so watch smaller diameter wheel doesn't clash. Wheel spacers would save the day but probably not wanted for this application (added stress on wheel bearings and corrupted steering geometry).
Pretty sure there's room in the arches for bigger, and rubbing there will be relatively easy to resolve I'd imagine (select large hammer....). A slight reduction in available steering lock won't kill you.
Ooops! (I have no sense of time....)