There's no need to misrepresent what Peter said regarding Paul's epistles.
15 And account that the longsuffering of our Lord is salvation; even as our beloved brother Paul also according to the wisdom given unto him hath written unto you;
16 As also in all his epistles, speaking in them of these things; in which are some things hard to be understood, which they that are unlearned and unstable wrest, as they do also the other scriptures, unto their own destruction.
What were "the other Scriptures"? Everything in the Hebrew Tanakh (the Law, the Prophets, and the Psalms). What we call "the Old Testament".
What does the word "other" imply? That the "first" Scriptures he is talking about are "all his epistles". All of Paul's epistles are being compared to, and equated with, the other Scriptures.
So is over half of our New Testament also the Word of God? Absolutely.
The "wisdom" mentioned by Peter should be taken to mean the wisdom given to Paul under the total control of the Holy Spirit so that what he was writing would be inerrant and infallible.
There are many today who claim for their own warped purposes in some cases Paul was merely expressing his personal opinions, therefore Christians can blithely disregard them. That is utter nonsense.