In 2015, Ramanathan played mostly on Futures and Challenger level. He entered Chennai Open where he lost in first round to Tatsuma Ito in straight sets. In April, he reached his first doubles final at a challenger event at Mersin Cup in Turkey. Partnering with Riccardo Ghedin, the pair lost final to Mate Pavić and Michael Venus. He entered his second ATP world tour event of the year at Malaysian Open where he lost in first round to Mikhail Kukushkin.