Assuming you're referring to the typical ITA wheel sizes...

1- 225/45 15's are essentially the same height as the more common 225/50 14. No ride height change results... and even if it did, you've got coilovers to adjust ride height.

2- Wheels and tires are cheaper on the used market due to increased commonality with other cars.

3- FD stays the same b/c of #1.

If you're comparing to the 225/50 the OP asked about, all of the common 15" sizes will lower the car and improve the effective FD. If you're comparing to something like a 225/50 13 then yeah... 15's would change things pretty drastically.