You are right bro, the spacer will do the job, but after compromising the comfort, and in long run damaging your suspensions
i will suggest that go for 15 with 195-55-R15 or 185-R15 with light weight wheels( Branded)
I am currently using the 195-55-R15 on 2007 vitz, and its working perfectly fine,with no compromise on fuel average.
as per manual they are also suggesting two sizes for vitz.