Mikrotik\RouterOS - simple VoIP prioritization - how to do it?

Question

VoIP

Good afternoon!
There are two offices connected by a tunnel (now l2tp, I will test GRE).
In office B there are cameras, in office A they are watched, only one at a time.
There are incomprehensible problems with VoIP in office B - no audibility, "croaking", although the channel is not selected even by half (5 out of 10 or 20 Mbps, there are two channels in office B).
Asterisk is located in office A, all VoIP traffic from office B goes through it.
Phones in a separate subnet, cameras too.
I want to try to set priorities - more phones, cameras - minimal, the rest - do not mark or touch.
With phones, I see two options:
1. Mark traffic from / to the subnet with phones.
2. Mark traffic from/to Asterisk. Correct me if it's not, but the whole voice should go through it.
The next question is about this:
wiki.mikrotik.com/wiki/Voip
And specifically about queues:

/ queue tree
add name="ether1_voip" parent=ether1 packet-mark=VoIP limit-at=0 queue=default priority=2 \
    max-limit=0 burst-limit=0 burst-threshold=0 burst-time=0s disabled=no
add name="ether2_voip" parent=ether2 packet-mark=VoIP limit-at=0 queue=default priority=2 \
    max-limit=0 burst-limit=0 burst-threshold=0 burst-time=0s disabled=no

1. Here, queues are hung on physical interfaces, while my traffic goes through a tunnel (with routing in mind) - this is either a PPP or GRE tunnel. Do I need to assign queues to it or is it enough only for WAN?
2. What is the default priority for untagged traffic in ROS? Those. in the example above for VoIP, the priority is two, for cameras I will make 8, and the rest of the traffic that I do not mark, what priority will it receive?