There is actually a huge difference between those two cards
http://gpuboss.com/gpus/GeForce-GT-630-vs-GeForce-GT-430
According to EA the game needs a GTX 650 or 5770 to run the game smoothly at low settings. http://help.ea.com/nz/article/fifa-15-pc-minimum-requirements/
Although its usually possible to play with a system just under minimum settings I honestly believe the nvidia GT 630 or Radeon 5570 are as low as you can go for FIFA 15 before parts of the game become unplayable. You might be able to find the Radeon 5570 cheaper than the nvidia 630 with a bit of luck.
Whats your current CPU/APU? Thats important too.