Will America be flooded in the next 15 years?
America is a very large country. The chance of it not suffering a flood somewhere in the country in 15 years is astronomical. In fact, I believe somewhere in the USA right this second, a leaking washing machine, overflowing bath or blocked drain is flooding a house.
Oh, you meant a biblical scale flood covering the highest peaks in the country? Given that is over 6000 meters, there is nowhere near enough water on the planet to do so. Short of an enormous icy comet arriving to deliver some more water, it isn't going to happen. Given a quick calculation suggests to gain an extra 6 kilometres of water worldwide, you'd need an icy comet just under 900 kilometres in diameter, so would probably qualify as a dwarf planet. Also, the one that helped wipe out the dinosaurs was about 10 km in diameter, so 900km diameter is bad news.
Or did you mean a flood of the type that gets reported in the news? 15 years without a major hurricane hitting the coast. or a big weather system ending up in the wrong bit of the hideously mismanaged Mississippi river system seems unlikely.
Not a significant portion of it. Coastal lowlands, harbors and barrier islands will likely see erosion, flooding and eventually, some will be submerged as sea level rises. But the vast majority of the land will remain above water. Which is not to say that rising sea levels are not a potential problem for all of us; we all depend on goods delivered to seaports, live sheltered from coastal storms by islands and salt marshes and expect high river levels to run off into the ocean. The changing climate will affect everyone.