I can confirm the crash happening on iPad mini 2 (A1490) with iOS 11.4 Minecraft version 1.5.1. The background image (beach) is at some points really laggy, at some points smooth, and game crashses at the menu. Sometimes you're able to get to the menu to open up a world, but trying to open a world also leads to a crash.
The issue appared in 1.5.1 when the background changed from underwater to the beach.
I play on a realm subscription to share a world with my family, so messing around with internet connection isn't really an option.
The issue actually seems to be partly fixed - for me - by iOS update to 11.4.1. After doing that, opening Minecraft reported a "crash detected, global resources reset", and now the background image (beach) seems smooth after some initial jerkiness (similar inital lagginess was with underwater and overworld images too, but it does still seem worse with beath). The game doesn't crash at the menu, and the realm can be opened and seems to work as well as before.
However, the game still seems to crash with opening offline worlds. It also crashes when closing the game with "Save & Quit", the last message on screen is "Loading Resources".
Redirected from MCPE-35940 to here, but judging from the symptoms this doesn't look much like the same issue. Maybe the underlying cause is the same, though. MCPE-35940 (and many duplicates) describes a condition specific to 1.5.1 on many iOS and some other devices where the background and menu often manages to load and crash happens after that.