You are experienced, so unless you ride fast wings or racewings (and you dont, the 683 starts early), dont go with the 12 m2.
On the common big wings used today, you can ride down to 7 knots if average weight, with a 12 m2.
But a 12 m2 can not hang in 7 to 8 knots, unless it is superlight, meaning strutless or aluula or something...
And even if, they got limited upper range on a foil, and turns slow.
Whereas a 10 m2 can go down to around 8 knots, and far more fun in every aspect, turns faster more peak power and better upper end.
Why do you keep your 15 m2 Turbine?
Seems pretty useless for foiling, sorry to say
And for snowkite you ride in even less wind also, isnt that a problem?
If you were a newbee on foil, the 12 could be fine, and used from 10 knots and up for learning, and when learned, you can sell it to another new rider, as it will be too heavy for the winds you can ride now, too slow, and too quickly overpowered.
But not being new, a 12 is something you should be reeeeeally careful about choosing.
So many dont use a 12 tube nowadays.
Either superlight strutless types, knowing they got very limited range, or foil kites instead.
Would go with a 10 m2 and be happy to have a "sweetspot" kite for most conditions.
Especially if the Ghost has good low end, then a 12 is not the choice as it will drop in the low winds you are able to ride in, and be a dog in terms of handling (again, assuming average weight).
A powerful 10 should be able to go down to 7-8 knots maybe, with long lines, and a lot easier to keep flying in your "holey" winds, than a 12.
And if you one day want to go low, get a totally different kite type
The listed windranges are of course useless, but that goes without saying...