Seems like world size and entity count is becoming a bigger problem in the latest versions. The latest version I experienced smooth performance in was in around 0.16.0. One of my worlds during 0.16.0 was a whopping 1.2 GB, and surprisingly, the game handled it pretty well, with barely any lag to be noticed. Since the official release updates, a world as big as 50 MB and a chunk with 20+ entities looks like enough to send the game into a crashing mess when trying to load chunks. My phone is an Android ZTE (Z987) GRAND X MAX +, and I've been using this phone to play MCPE since (I think) 0.7.2, and until the official release updates, the game has been running smoothly. I'm not sure if it's my phone that's having trouble running the game, or the game itself.