According to LDS, is the Apostle Paul wrong that remaining unmarried is spiritually better than being married?

Paul was not against marriage, as he made other statements (1 Timothy 3, Titus 1:5-9) for marriage and he was probably married (though widowed? at the time of epistle to Corinthians, see below).

From How can Paul's views be reconciled with the revealed truths of eternal marriage?

Paul’s teachings, as recorded in letters that were sent to churches and saints in various stages of spiritual progression, reflect the character and experience of a man who understands family relationships and can speak with authority on the subject.

In the first place, Paul himself was likely to have been married because of his Judaic background. In his defense before the Jewish crowd outside the Roman barracks of the Antonian tower, Paul states that he was taught according to the perfect manner of the law of the fathers and was zealous in living that law. (See Acts 22:3.) Again, in his defense before the Pharisees and Sadducees, Paul claims that he is a Pharisee, the son of a Pharisee. (See Acts 23:6.) To the Galatians, Paul had written that he was more zealous in fulfilling the requirements of his religion than others of his time. (See Gal. 1:14.) The emphasis that the Jews put on marriage as part of their law and tradition would certainly have been used against Paul in view of such statements if he had not been married.

Further evidence that Paul was married is found in the likelihood that Paul was a member of the Sanhedrin. One of the qualifications for becoming a member of that body was that a man must be married and the father of children, which was thought to make him more merciful in dispensing justice in the courts. ... In view of these evidences, most non-Mormon scholars do not argue that Paul had never been married, but that he was either divorced or was a widower by the time he wrote to the Corinthian church.

But let us take a closer look at 1 Corinthians 7 to see if the evidence supports this last conjecture. At the outset, Paul refers to a letter the Corinthians wrote to him: “Now concerning the things whereof ye wrote unto me: It is good for a man not to touch a woman.” Although the King James Version does not make it clear who makes the statement, “it is good for a man not to touch a woman,” the Greek text and the Inspired Version both make this a statement of the Corinthians. We do not know the context of this statement, because we do not have the Corinthian epistle to Paul. The only context we can supply is Paul’s answer and, fortunately, that does give us some clue as to their problem. Paul wishes (see 1 Cor. 7:7) that all men were as he was. But what is that? Could it be that he wishes all men were divorced or that all had lost their companions in death, or does he simply wish that men would be so dedicated to the work of the Lord that they be as though single?

Evidence of the latter possibility can be found later in the chapter. In verses 10 and 11, [1 Cor. 7:10–11] Paul does not tell the married saints to become separated, but if they are separated, he suggests either that they remain that way rather than marry someone else or that they become reconciled. Paul even enjoins against separation in part-member families if the husband and wife are compatible (1 Cor. 7:12–14), because the member may someday be able to help save his spouse (see 1 Cor. 7:16).

One reason Paul wrote to the Corinthians concerning these matters is found in verse 29 [1 Cor. 7:29], where he states, “this I say, brethren, the time is short: it remaineth, that … they that have wives be as though they had none.” He further states (1 Cor. 7:32) that the unmarried saints (and those who are as though unmarried) care for the things of the Lord, but too often a married person puts other things before the work of the Lord (1 Cor. 7:33). Paul is simply reminding those who have been called to God’s work to put that calling first, even before earthly matters.

In the Inspired Version, Joseph Smith made an important addition to 1 Corinthians 7:29 [1 Cor. 7:29] that supports this interpretation: “But I speak unto you who are called unto the ministry. For this I say, brethren, the time that remaineth is but short, that ye shall be sent forth unto the ministry. Even they who have wives, shall be as though they had none; for ye are called and chosen to do the Lord’s work.” Contrary to generally accepted interpretations, Paul is not condemning marriage in this chapter but is evidently replying to a problem regarding missionaries who desire to become married. His advice is that while they are on their missions (and he declared that the time for missionary work is short) they should be concerned with the work of the Lord and not with family or personal matters.

Concerning the importance of marriage for a member of the church and the relationships of family members toward each other and the Lord, Paul exhorts the saints to be followers of himself, especially in the ordinances of the church. (See 1 Cor. 11:1–2.) He teaches that the husband is to honor the Lord as his head and the wife is to honor the husband as her head, and that “neither is the man without the woman, neither the woman without the man, in the Lord.” (1 Cor. 11:11.) ...