In our iOS app we use a MKTileOverlay subclass and set tileSize to CGSizeMake(512, 512). This allows tiled maps such as Open Street Maps to display larger for those that need larger font sizes.
Since iOS 15 this no longer works, and the tiles are not large anymore and are small, similar to how it was before we added this feature.
Once tileSize has been set, we use loadTileAtPath:(MKTileOverlayPath)path result:(void (^)(NSData *, NSError *))result to return the larger image NSData in the result.
Did something change in OS 15 and MKTileOverlay and tileSize that would require some changes on our end?