You cannot join modern Realms or servers. You also miss modern features like The End dimension (added in 0.16). Your worlds will not convert forward to v1.x without severe chunk corruption.
This build was part of the "Friendly Update" development cycle. Pocket Edition v0.15.0 alpha - Minecraft Wiki download minecraft pocket edition v0.15.0 alpha build 2
Get Minecraft: Pocket Edition v0.15.0 Alpha Build 2 Take a trip down memory lane with one of the most pivotal updates in Minecraft PE history! The v0.15.0 Alpha Build 2 You cannot join modern Realms or servers
None. Mojang Studios and official app stores (Google Play Store, Apple App Store) no longer distribute Alpha builds. Users attempting to download this version through official channels will be redirected to the current version of Minecraft (Bedrock Edition). This build was part of the "Friendly Update"
For the first time in Pocket Edition history, redstone engineers could build moving contraptions. This build fully implemented pistons, allowing for hidden doors, elevators, and crop harvesters. It was a game-changer for mobile redstone.
Always scan APK files for malware and never log into your Microsoft account on legacy builds that may not support modern encryption.