He reached the semifinals of the 2015 French Open boys' singles event, losing to Taylor Fritz.

In June, Denolly made his Grand Slam doubles debut at the French Open, partnering with Alexandre Müller.

In June, Denolly won his maiden Challenger title in Blois, partnering with Alexandre Müller.

In September, Denolly played his second Grand Slam match at the French Open, partnering with Kyrian Jacquet.

the pair lost in the first round to future semi-finalists Juan Sebastian Cabal and Robert Farah.