Vendor Name : Fairphone
Device name : Fairphone 3
Device CodeName : FP3
Version of /e/OS which existed previously : 3.0.4-a14-community
Current version of /e/OS : 3.0.4-a15-community
Device Not rooted
I successfully did the upgrade from a14 to a15 with adb sideload without any data loss. In my case, my bootloader is locked (reason : Fairphone - FP3 - FP3+ Documentation Suggestions - #79 by Mamalo) and it causes no problems.
In my case, just one bug : the navigation hint is shown permanently (also reported by @urs_lesse ) above :