>A Pokémon with this Ability will wake up if it is asleep in battle (such as if it gains the Ability outside of battle or by an effect like Skill Swap, or is put to sleep by a Pokémon with an Ability like Mold Breaker). If the Pokémon is holding a Chesto Berry or a Lum Berry, it will be eaten before Insomnia wakes up the Pokémon.
Yes, if Mewtwo mega evolves into Mega Mewtwo Y, it will wake up if it is asleep.
Source