fun prefetchZoomDelta(value: Long = 4L): ImageSource
val prefetchZoomDelta: Long?

When loading a map, if PrefetchZoomDelta is set to any number greater than 0, the map will first request a tile at zoom level lower than zoom - delta, but so that the zoom level is multiple of delta, in an attempt to display a full map at lower resolution as quick as possible. It will get clamped at the tile source minimum zoom. The default delta is 4.