WASHINGTON—Newly released transcripts show that many Federal Reserve officials had concerns in late 2015 over whether they were making a mistake in raising a key interest rate for the first time in nearly decade. Transcripts of their discussions, released Friday, showed that the chief concern was whether the Fed would be acting prematurely in starting to raise rates given how low inflation was at the time. In the end, the Fed unanimously approved a quarter-point hike in its policy rate, the first change in the rate since the central bank slashed it to a record low of 0 to 0.25 percent in December 2008 at the height of the financial crisis. During their debate on the change, many officials expressed worries that the small rate hike was being made even though inflation for the past six years had fallen below the Fed’s 2 percent target. The Fed manages interest rates …