My conclusion is that it is possible, and indeed should be our goal to live a sinless life in this world. You stated this is not possible, directly contradicting the word of God.
Grace is always available, yes. "If we confess our sin he is faithful and just... (1 John 1:9)"
No, we do not lose our salvation if we sin again, and we do need to be washed, from time to time, of the contamination of this world. BUT... "If we sin willfully after we have received knowledge of the truth there remaineth no sacrifice for us [Hebrews 10:26]."
Let me give you an example of the danger of saying, "We sin, we repent, we are forgiven."
Reg came to me and said, "If a woman proposed to me for sexual pleasures, I would do it, and then repent, and know that I'm okay." That is sinning willfully. I told him very plainly that he not only would not be okay, he was not okay, and in danger of hellfire.
Now... we may not SAY the same as Reg, but do we DO the same as Reg? If you have a problem with scantily clad ladies on the beach, should you not ask God to reveal the victory that is in you through Jesus Christ? "For, by grace you have been saved... unto good works... [Eph 2:8 & 10]" Why remain in the quandry of Romans 7 when Paul has already given you the solution, "Who shall deliver me from this body of death? I thank God, through Jesus Christ... [Romans 7:24-25].
Your conclusion drawn from 1 Corinthians 15 is incorrect. This passage speaks not of salvation, but of resurrection.