I think 15" would be small, instead they may give 16" steel wheels on base version and 17"/18" alloys on top version. The alloys in the spy shots are 18" ones.
From what i had read those alloys seem to be 17 inch on international versions not 18 inch.
In post#99 on this thread the first pic shows two different alloys on front & back!
So two sizes 16 inch alloys & 17 inch Alloys mite be on offer depending on variant.
Its possible spare wheel will be the only steel wheels.
Re-Posting pics below