But you can avoid that with a few settings:
1) In SongBook+ settings select "Media player", then disable the 5 switches "Allow playback of sound file 1-5".
2) In SongBook+ settings select "Metronome", then disable the switch "Enable acoustic metronome".
With these settings in SongBook+ the latency in Turbosounds app should go back to 1.5ms or 2.9ms.