What i did was use a Gossifleur that was at least strong enough to survive one hit. It's ability reduces opponents speed on contact so i reduced Lopunnys speed by 2 stages and after that i pretty much threw half my team at it with other stat reducing moves and used my Luxio to just bite it down. Yes i had to be one lvl above the gym to evolve it at lvl 15 but that Lopunny definitely has boostet stats so i don't even feel bad about it