I cannot find the paper right now (the CEREGE research center's website is down?) but several news sites echo that in only 350 years, beginning 14,600 years ago, sea levels rose as much as 14 meters, judging from coral formations near Tahiti (Polynesia).
That means on average 1 meter each 25 years. The actual impact of this kind of change varies depending on the relief of the coast but nowadays one such change of just one meter would swallow about 1/3 of the Netherlands, for example.
Sources: CNRS, Pileta[es].