Ver. 15. "So then, brethren, stand fast, and hold the traditions which ye were taught, whether by word, or by Epistle of ours."
There's nothing in that verse about an infallible body of Bishops or unwritten teachings. That is one of the earliest writings of the New Testament. What did Paul tell the Corinthians at a later date?
1 Corinthians 4:6 - I have applied all these things to myself and Apollos for your benefit, brothers, that you may learn by us not to go beyond what is written, that none of you may be puffed up in favor of one against another.
Luke 1:1-4 - Inasmuch as many have undertaken to compile a narrative of the things that have been accomplished among us, just as those who from the beginning were eyewitnesses and ministers of the word have delivered them to us, it seemed good to me also, having followed all things closely for some time past, to write an orderly account for you, most excellent Theophilus, that you may have certainty concerning the things you have been taught.
That doesn't follow from those passages either. How do you know that the unwritten teachings of St. Paul were later written down?
Also, the bishops are only infallible to the extent that they hew to the truth of tradition which includes Scripture but is by no means limited to it. Infallibility is in the Church as a whole, clergy and lay.
Basically this prooftext war is just going to go around in circles as long as you're talking about it in generalities. This needs to be discussed in terms of concrete examples.