2915 is a/b/g
2200 is b/g
if you do not have a wireless "a" router, then just get the 2200 and save yourself $10 to take your wife out to mcdonald's for that special occasion
wireless "a" is more expensive, if you are in a high 2.4-2.5Ghz (i.e. you got a lot of cordless phones on all the time at home) you may want the wireless "a" which operates at a higher frequency. but there is really no reason to get it, unless you have wireless "a". most hotspots will have b or g anyways not a, for the cost reason.
yeah, brain fart on my part...although in the ranting text i noted 2200 as non-"a" very confusing and i should only speak when i'm spoken to