why games like asphalt 8 aren't smooth?

i played Real racing 3 and asphalt 8 on my device and the game isn't smooth and lagging a bit , unlike my old Note 2 which was running it a bit better than what i saw on Z2 , is it about optimization with Snapdragon 801? and if there is a fix for Asphalt 8 (especially) can some one provide it? thanks in advance .