Percy writes:
If the earthquake was 150 miles from shore...
It wasn't. It was 130 Km from shore, which would make it about 80 miles.
...and if tsunami's travel at 500 mph...
Only in deep sea, the moment it gets shallower, their speed decreases, reaching a maximum of about 80 Km (50 miles) per hour.
On the one hand it feels very dire to me, but on the other we know that Japan takes the threat of tsunamis seriously and no doubt has detailed evacuation plans for the coast.
Reports of a wave 10 meters (33feet) high reaching and flooding Sendai airport are as early as 15:55. Given that the Earthquake began at 14:46, that leaves only 9 minutes from the first tremors until the tsunami was hitting the land. Regardless of how efficient you are at evacuation, I don't think that is sufficient time.