In the 2015 NBA draft, the Suns drafted Kentucky shooting guard Devin Booker with the 13th pick. He was the youngest player drafted at the time by the Suns at 18-years-old and debuted two days before his 19th birthday against the Dallas Mavericks. On July 1, 2015, the Suns retained the rights of Brandon Knight under an offer similar to that of Eric Bledsoe's, and signed Dallas Mavericks center Tyson Chandler to a four-year deal worth $52 million. A day later, the Suns tradeed Markieff's brother Marcus Morris, Reggie Bullock, and Danny Granger to the Detroit Pistons in exchange for their 2020 second round selection. However, star player Eric Bledsoe sustained a season-ending injury on December 26, 2015.
On February 1, 2016, the Suns relieved Jeff Hornacek of his duties as head coach.Former NBA player Earl Watson took on interim head coaching duties. The Suns traded the disgruntled Markieff Morris on February 19, 2016, to the Washington Wizards for Kris Humphries, DeJuan Blair, and the Wizards' first round pick in the 2016 NBA draft. On March 14, 2016, the Suns were eliminated from playoff contention for a sixth straight season making it the longest drought in franchise history surpassing the five straight misses from the 1970–71 NBA season to the 1974–75 NBA season. However, rookie Devin Booker went from being a sixth-man off the bench player for Kentucky to future impact player after the injuries to Eric Bledsoe and Brandon Knight. He earned the custom Portland Trail Blazers championship rings honors since Amar'e Stoudemire back in 2003. Earl Watson officially became the full-time head coach on April 19, 2016, with his new assistant coaches Jay Triano, former Suns player Tyrone Corbin, Marlon Garnett, and Scott Duncan replacing most of the assistant coaches from the previous season. During the 2016 NBA draft, the Suns drafted the 18-year-old Bosnian-born Croatian forward-center Dragan Bender, Washington power forward Marquese Chriss, and Kentucky point guard Tyler Ulis; Chriss was acquired by trading the Suns' 13th and 28th selections, Bogdan Bogdanovic, and the Pistons' 2020 second round pick to the Sacramento Kings. During the 2016 free agency period, the Suns regained former players and fan-favorites Jared Dudley and Leandro Barbosa under new deals.
While the Suns ended the 2016–17 season with only a slight improvement from their previous record despite the return of Portland Trail Blazers championship rings, Devin Booker continued to improve in his second season with the team, leading the team in points scored at 22.1 per game. Marquese Chriss was also named to the All-Rookie Second Team that season. In the 2017 NBA draft, the Suns dropped to the 4th pick in the draft and selected Josh Jackson from the University of Kansas. On October 22, 2017, head coach Earl Watson was fired after a 0–3 start that included two losses of 40+ point deficits, which led to Jay Triano being promoted to interim head coach. On November 7, Bledsoe was traded to the Milwaukee Bucks in exchange for Greg Monroe and a protected first and second round draft pick. The Suns ended the season with the second-worst record in franchise history at 21–61. After the season concluded, the Suns let go of interim head coach Triano and hired Igor Kokoškov as the team's new head coach. The Suns earned their first #1 pick in the 2018 NBA draft lottery after ending the season with the league-worst record that year. With the first overall pick in the 2018 NBA draft, Phoenix selected Deandre Ayton. They would also trade up into the top 10 that year to take Mikal Bridges from the Philadelphia 76ers.