Hi Clifford,
I am not a doctor or dietician, and I would encourage you to check with your Doctor about this if you have any concerns.
Based on my limited
experience and an article from St. Mark's Hospital. It seems to be fairly common that people in your situation can get back to a fairly normal diet within a few months. Just introducing things slowly, and obviously starting with soft foods right after surgery. Since you say you are 15 months out, I don't see why walnuts would be any different than most other normal foods? They are high in good fats and proteins.
Is there any specific concern about walnuts that you have? Have you had any trouble with any other solid food items?
"The future is something which everyone reaches at the rate of sixty minutes an hour, whatever he does, whoever he is." C.S. Lewis
"When the whole world is running towards a cliff, he who is running in the opposite direction appears to have lost his mind." C.S. Lewis