Update - Did you use smart switch when setting up you new phone? If you did that might be the promlem I have been having theses sort of issues since the phone was released and kept clearing the cache which did help but it was still unstable and it still crashed at random times throughout the day and night
But yesterday I bit the bullet and compleaty wiped my phone and did not copy anythink through this time just re-set up fresh and so far it's been great now and seems much snapper like a completely different phone... I put it off for so long as I had a lot of things to redo but it has fixed it now I am sure... Give it a try and good luck.
