Why does my Nexus 5X lag so much?

[Dark Ghost117z]

I just bought a Nexus 5X and I thought it was going to be really good. I'm not saying it's not a good phone, but it doesn't meet my expectations. It has 2GB of ram and a 808 Snapdragon 1.8GHz 6 core CPU, and that's really good. It seemed good at first, but so many games lag like: Mortal Komabat X, fallout shelter, and smashy road. Games like that are laggy. I really just want to know if it's because the games are not optimized for the Nexus 5X or if it's just my phone.