Dear friend, take a closer look at this passage and those printed before and after it, to place it in its proper context.
In 2 Tim. 3:15 - Paul appeals to the sacred writings of Scripture referring to the Old Testament Scriptures with which Timothy was raised (not the New Testament which was not even compiled at the time of Paul's teaching). This verse also proves that one can come to faith in Jesus Christ without the New Testament.
In 2 Tim. 3:16 - this verse says that Scripture is "profitable" for every good work, but not exclusive. The word "profitable" is "ophelimos" in Greek. "Ophelimos" only means useful, which underscores that Scripture is not mandatory or exclusive. You unbiblically argue that profitable means exclusive.
In 2 Tim. 3:16 - further, the verse "all Scripture" uses the words "pasa graphe" which actually means every (not all) Scripture. This means every passage of Scripture is useful. Thus, the erroneous reading of "pasa graphe" would mean every single passage of Scripture is exclusive. This would mean Christians could not only use "sola Matthew," or "sola Mark," but could rely on one single verse from a Gospel as the exclusive authority of God's word. This, of course, is not true and even you would agree. Also, "pasa graphe" cannot mean "all of Scripture" because there was no New Testament canon to which Paul could have been referring, unless you argue that the New Testament is not being included by Paul.
In 2 Tim. 3:16 - also, these inspired Old Testament Scriptures Paul is referring to included the deuterocanonical books which the Protestants removed from the Bible 1,500 years later.
In 2 Tim. 3:17 - Paul's reference to the "man of God" who may be complete refers to a clergyman, not a layman. It is an instruction to a bishop of the Church. So, although Protestants use it to prove their case, the passage is not even relevant to most of the faithful.
In 2 Tim. 3:17 - further, Paul's use of the word "complete" for every good work is "artios" which simply means the clergy is "suitable" or "fit." Also, artios does not describe the Scriptures, it describes the clergyman. So, you cannot use this verse to argue the Scriptures are complete.
If you are going to quote Scripture, place it within its proper perspective, including all of the verses.