I cannot believe that this thread has gone this far.
I read it in the beginning, but only when thought of the storage tanks were for DHW for faucet.
First, my house is comparable.
4000 sq ft with an attic (third floor) 1200 approx sq ft that is not insulated
Pretty much whole house is not insulated, some parts have blue foam sheets put on the siding,
and then vinyl siding over top, but that is just "some parts"
Next i have an addition 600+sqft with mostly windows, and then 600 MBR on top of that, mostly windows.
Drafty windows, doors, basement, attic, and any other place you can think of.
I have an EFM 520, so I am in the same boat.
Just judging by the pic, I think your house is a bit bigger, but you say somewhat insulated.
our heat loss should be similar.
Dead of winter I get an ash bin about 12 hours or so.
I went through 10 ton last winter, 1.5-2 ton summer DHW
NOW, my stoker comes on as soon as the thermostats call for heat.
I have two zones, one 120+ ft cast iron baseboard, one 10 or so standups.
I will say this, when there is a heat call, that stoker needs to come on.
When there is a heat call, that water in the radiators is cold or just about.
There is some shock, but the sooner that stoker comes on, the better.
The stoker comes on and is fire puffing when it needs to.
IT WILL HIT THE LL when there is a call for heat. IT WILL
So it needs to start stoking right away.
In the dead of winter with it calling for heat and stoking away, then it runs pretty good (and eats coal pretty good)
But it is the average of what I have always heard.
My coal cost is about 30-40% of what oil was.
Plus I keep TT set higher.
15 ton may seem high, but you may want to check out what is above you.
Is your attic insulated?
You could have more heat loss than you think.
If you want 24/7 circ, that may help you out, but think about what the house previous consumed.
Convert it to coal to see if the numbers match up.
I am not aware of in floor radiant heat or consumption of coal from it,
but I have heard that it has a huge load.. something to consider, if you do not have that hooked up yet.
If any and all heat calls will bring it to the LL, then you need it set like you have it.
Other wise it will just take longer to satisfy the TT.
HOWEVER, with my drafty house, I def need it this way.
You mentioned that a TT satisfy will stay warm for a while...but you never
mentioned if every heat call brings it to the LL.
Hope some of this helps, sorry if it doesnt.