I've been training an uber team and Kyogre was extremely easy to level up after I leveled it up a couple of levels. I trained against my rival in Battle Park (by changing the clock to allow me to battle him again and again) and Kyogre was capable of OHKOing all of his Pokémon. Ice Beam takes care of Roserade and Staraptor, Water Spout OHKOs Rapidash, Snorlax and Heracross and Thunder OHKOed Empoleon. Add a Lucky Egg and boosted experience because its OT isn't the same as mine and you'll have a level 100 Kyogre in 2 hours.