Possibly. I haven't played MW3, but unless it's reporting raw ping times it might say it's "good" but really has up to 150ms or something rediculous like that. Cellular connections are generally poor for pings compared to wired broadband, and if you're playing over wifi that can add to the latency as well (and won't be reported by the game). People's sensitivities to wifi latency are all over, so YMMV on that bit.
Anyway, if you're on a cellular or similar wireless connection, I wouldn't count on a lag-free experience. And if MW3 is still P2P instead of running dedicated servers, well, that's just rubbing salt into the wound.