lets talk about thermal time constants.
A cubic meter of copper has 9,600 seconds thermal time constant, with 4 of the 6 faces insulated, and heat applied and removed from 2 opposite faces.
We can chop the cubic meter into 0.1 meter columns, and then into 0.1 meter cubes, and we learn the time constant has sped up by 100X, to 96 seconds.
Chop more, into 1cm cubes, and you now have 0.96 second time constant.
Your 45 cm wire (even assuming NO HEAT FLOW from the wire along that 45cm distance, will have approx. 0.96 * (45 * 45) = 2,000 seconds time constant.
Thus the misbehaving ADC will not be caused by soldering iron heating.
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4 of 6 faces ----- start with any face, exit any edge and continue in that direction until you return to the original face; now insulate the 4 faces you traveled thru.
time constant: compute the thermal resistance of one meter cube; compute the thermal storage of that 1 meter cube; multiply those 2 numbers.
The inverse of what you computed is also called "thermal diffusivity".