You should be able to reduce latency under 10s by adjusting settings as documented at https://www.wowza.com/forums/content.php?88-How-to-configure-Apple-HLS-packetization-(cupertinostreaming)#mgrlive :
Cupertino segmenter property reference
cupertinoChunkDurationTarget - Sets the duration of each chunk in
milliseconds. If you're using Origin/Edge configuration this will need
to be set on the Origin and Edges with matching values.
cupertinoMaxChunkCount - Sets the maximum number of chunks stored in
the available chunk list.
cupertinoPlaylistChunkCount - Sets the number of items returned in the
playlist.
cupertinoRepeaterChunkCount - Sets the number of chunks that are
immediately sent from the origin to the edge after initial connection
and is configured on the origin. This property is only required for
use with Live Edge applications. A live edge application will have a
StreamType of liverepeater-edge in the Application.xml file.
Try with smaller chunks (2000ms) and low chunk count to reduce possible latency.