The Labyrinth "minigame" is laggy for you too, huh? Word of advice, be patient and pay attention to the button you click before moving again. Since it lights up when you click it, you can use that to your advantage and wait for it to load if it's already lit up. (Should probably note I play the game on mobile)
Also, if you wanna grind levels, Mimics are gonna grant you more Exp than anything else. Just spam Seduction on them, since Mimics will always be an equal level to yourself, it's better to play it safe with them. Once you get past the Labyrinth, you'll be able to "Explore" the Labyrinth, and that's gonna be your level grinding spot after that point, since turning on Nightmare Mode when exploring there makes every enemy equal level to you, just like those Mimics you would grind beforehand.