Let the thousands, hundreds, tens, and units digits of the number be $$a$$, $$b$$, $$c$$, and $$d$$, respectively.
The sum of the digits in the thousands, hundreds, and tens places is 15; $$a+b+c = 15$$ .....(1)
The sum of the digits in the hundreds, tens, and units places is 16; $$b+c+d = 16$$ .....(2)
Solving equations (1) and (2), we get $$d = a+1$$.
The digit in the tens place is 6 more than the digit in the units place; $$c=d+6 = a+1+6 = a+7$$ .....(3)
Substituting the value of $$c$$ in terms of $$a$$ in equation (1), we get; $$a+b+a+7 = 15$$ or $$b=8-2a$$
Thus, the number is: $$\underline{a}\text{ }\underline{8-2a}\text{ }\underline{a+7}\text{ }\underline{a+1}$$
We know that since the number is a four digit number, $$a\geq 1$$. But all the four digits have to be less than or equal to $$9$$ but greater than or equal to $$0$$, thus,
$$8-2a\geq 0$$ gives $$a\leq 4$$ and $$a+7\leq 9$$ gives $$a\leq 2$$.
Thus, $$a$$ can be $$1$$ or $$2$$.
The two possible values for the number, therefore, are, $$1682$$ and $$2493$$, when we put $$a=1$$ and $$a=2$$, respectively.
The difference between the only two possible values is, $$2493 - 1682 = 811$$
Option A is the correct answer.