Hi,
did you do an error calculation? or at least an error expectation?
If you do this, you will recognize, that the buffer doesn´t give a benefit. It just introduces errors.
Scaling down 0...15V with 1M/20k gives an output voltage of 0...294mV.
Then the offset error of the MCP6002 is +/-4.5mV wich is 9mV in total. this is an error of 3% full scale.
(or about 10% at referenced to 5V input, or about 50% at 1V input.)
So the 0.1% resistors are useless.
Then there is a 25mV OPAMP output voltage limit (maximum) to the rails.
This makes a measurement of input voltages of 0...1.2V completely impossible.
--> Use a voltage divider of about 75k and 10k and a capacitor (parallel to the 10k) without buffer and get far better performance. Especially with low input voltages.
Klaus
Btw: MCP6002 is a dual OPAMP. What did you do with the second OPAMP? Hopfully you did not leave the unused inputs floating...
The same applies for the unused inputs of your ADC.
Indeed it applies for any analog or digital circuit....if not mentioned otheriwse in the datasheets.