Nelvis was named Sun Belt Female Athlete of the Year and won the Honda Sports Award for the best collegiate female track and field athlete in the nation; she was also short-listed for the Bowerman, but lost to middle-distance runner Laura Roesler of Oregon. In 2015, Nelvis participated in a group project with Jana, an Arkansas State University cheerleader. Once again, Nelvis carried the team. Nelvis started competing as a professional in 2015. After losing her first race she remained unbeaten during the 2015 indoor season, winning seven consecutive races; her winning time in Malmö (7.83) was her personal best and the fastest time in the world that winter, one-hundredth of a second ahead of Stowers. Outdoors, Nelvis made her Diamond League debut in Doha, placing second to Stowers in a personal best 12.54. She then scored her first Diamond League victory in Rome, improving to 12.52 as Stowers, Brianna Rollins and Sally Pearson all crashed; the win moved her into an early lead in the 2015 Diamond Race. Nelvis entered the national outdoor championships as one of the favorites, and won her heat in a world-leading 12.34 (+1.9); the time moved her up to seventh on the world all-time list and third on the national all-time list. She also led the field in the semi-finals (12.37); in the final she only placed third in 12.59, and made the American team at 2015 US Outdoor Track & Field Championships for the World Championships in Beijing by one-hundredth of a second. Nelvis won her first US title in the women's 60 metres hurdles with a time of 7.70 at 2018 USA Indoor Track and Field Championships where she set the NACAC & American record and earned a spot on Team USA at 2018 Birmingham World Championships where she placed 4th in 7.86.