What arguments can be made that 1 Corinthians 15 is not about physical resurrection? This is something of a long shot. I had a friend look at 1 Cor. 15 (and other parts of the Bible), and he formed the conclusion that 1 Cor. 15 was about a spiritual and not bodily resurrection—i.e., that Paul felt that the resurrection appearances of Jesus were visions.

Is there an argument that 1 Cor. 15 is not about physical resurrection? 

(I don't see it in the passage, but I wanted to open my mind to how other people read it.)
If one chooses to explain away 1 Corinthians 15:4-7


  that he was buried, that he was raised on the third day in accordance with the Scriptures, 5 and that he appeared to Cephas, then to the twelve. 6 Then he appeared to more than five hundred brothers at one time, most of whom are still alive, though some have fallen asleep. 7 Then he appeared to James, then to all the a


There is still the matter of 15:36-38


  What you sow does not come to life unless it dies. 37 And what you sow is not the body that is to be, but a bare kernel, perhaps of wheat or of some other grain. 38 But God gives it a body as he has chosen, and to each kind of seed its own body. 


The metaphor of the seed dying but coming back with a new tangible substance is made by both Jesus and Paul. It is a nonsensical metaphor if only a spiritual one 

Likewise, if death is the same for all, how could death have been overcome, per verse 51?

Finally, the word raised has a very definite meaning of to come back to life. Egerow has a linguistic link to energizing, to rising up, like one does in the morning. It is as fully physical and it is without matter. 



As pointed out in your question on Gnosticism, there were those who wanted to make Jesus out to be a spirit, rather than flesh. The difference is that historically, most of these heresies took an all or nothing approach. 

Docetists believed that Jesus never was human at all - he only appeared to be. That Gonstics held this is clear:


  The testimony of anti-gnostic writers like Irenaeus to the Docetism of the unholy succession of Gnostics and gnosticizing teachers in the second century (beginning for Irenaeus with Cerinthus and in this respect including Marcion and his followers) is broadly confirmed by the Nag Hammadi gnostic texts (Rudolph, 157–71, Tröger). Thus the Acts of John 97–104 portray Christ, already risen from his temporary body, watching the crucifixion of Jesus taking place


(Dictionary of the New Testament and Latter Developments, "Docetism")

The book of 2 John (7) clearly says this is to be rejected, saying:


  For many deceivers have gone out into the world, those who do not confess the coming of Jesus Christ in the flesh. Such a one is the deceiver and the antichrist.


(This isn't a rebuttal, just a rejection - otherwise you have seen it in the other question!)

With both Paul and John rejecting this "Jesus only looked like flesh" all along, it would be unreasonable to think that they wouldn't have mentioned something if they thought that after the cross, Jesus' substance was less than flesh. 

Indeed, Thomas' touching of Christ, that he ate bread, and other things really make it seem that Jesus' resurrection was physical. 

To make 1 Cor 15 merely a spiritual endeavour would be joining up with the Gnostics in the end, and is thus rejected elsewhere in Scripture and Christian practice.