don't know the exact values of N and T

For one thing N=1 T=1 trivially satisfies your condition...

I'm not sure what you mean by this.

I mean, suppose that you got yourself a function that takes in a description of what's going on in a region of spacetime, and it spits out a real number of how bad it is.

Now, that function can do all sorts of perfectly reasonable things that could make it asymptotic for large numbers of people, for example it could be counting distinct subjective experiences in there (otherwise a mind upload on very multiple redundant hardware is an utility monster, despite having an identical subjective experience to same upload running one time. That's much sillier than the usual utility monster, which feels much stronger feelings). This would impose a finite limit (for brains of finite complexity).

One thing that function can't do, is to have a general property that f(a union b)=f(a)+f(b) , because then we just subdivide our space into individual atoms none of which are feeling anything.