Koi suspension nai kharab hoti if you keep the tyre diameter same.. original size is 195/65/R15 which is 635mm.. fuel economy is not affected by rim size, it is affected by width of tyre.. any thing above 195 will reduce fuel economy unless the better brand has less rolling resistance than General tyres (no way to find out with out actual trial)..
if you can afford 17" rims n low profile tyre then go with it or get 16", warna original 15" wala hi use karlo..
these sizes wont affect the suspension:
225/45/R17 (this will reduce fuel efficiency)
225/50/R16 (this will reduce fuel efficiency)