2015 Donati's first big professional result came in
Naples at the
2015 Tennis Napoli Cup. As a wildcard, the Italian defeated
Axel Michon in straight sets in the first round, World number 111 (former n. 33) and number 1 seed
Andrey Golubev 6–7(3), 6–4, 6–2 in the following round, and fellow Italian
Andrea Arnaboldi in a thriller three-setter in the quarterfinals. Donati then reached his first
ATP Challenger Tour final (beating
Marco Cecchinato 7–6(5), 6–2 in the semifinals) where he lost to
Daniel Muñoz de la Nava in straight sets. In May Donati obtained a wildcard into the main draw of the
2015 Internazionali BNL d'Italia, in Rome. Playing for the first time in a Master 1000 tournament (also his first ATP match), Donati fought back – from a set down – to beat World number 49
Santiago Giraldo 2–6, 6–1, 6–4. ==ATP Challenger and ITF Futures finals==