Mesh segmented message long roundtrip time

Hi Nordic Team

I encounterd the following behaviour:

Segmented message took 8s for acknoledge state.

I did the following:

Setup: 2 Devices NRF52840DK, provisioned and configured one groupadress to write/listen on.

TTL = 4, acknoledged message. No Gatt connection active, but advertising.

Code: Based on NRF Mesh SDK 5.0 (i know, no more developement on this)

->Send message 14byte payload so segmented message is nescessary.

<-then wait for Ack. this takes 8s from send to ack.

When sending unacknoledged the busy flag stays the same time on busy (status = 8).

This can be confirmed on the receiving side as well.

I  also monitored the traffic with the mesh sniffer APP, there the publish message needs 2 seconds.

Question:

what does consume this much time? where can i optimise the round trip time?