We are used to that. We can't understand how its possible to have a break of 3 hours .
Musaf takes around 4 hours. We don't go very slow but we don't go fast neither. Maybe we are saying more פיוטים then חב"ד? I'm not sure.
I guess it also depends on the size of the shul ?
My shul had a similar start time and break (though between mussaf and mincha, not shachris and mussaf), and I've had YK elsewhere that started earlier and ended later with absolutely no break. But this just sounds like poor planning.
The planned part is that you daven slow all the תפילות besides mincha. So it all depends how much time is left for mincha.
Is there a rov in the shul that approves of that mehalech? It just seems backwards.
The baal tefillah for mincha in our shul is very much not a chazan, and goes what I would consider fast. Yet I could never imagine spending only 10 minutes for chazaras hashatz, with slichos, viduy, avinu malkeinu, etc.