Airbnb’s years-long effort to crack the market for vacation tours and activities accelerated this year in what was known internally as the “summer of love.” After testing the service extensively, the company looked to grow its Experiences business rapidly, offering bar crawls, hat-making classes and other trip add-ons to more than 1,000 cities from Abu Dhabi to Reykjavik.

But hand-picking the activities available to travelers has kept the business small for now: Experiences pulled in roughly $15 million in revenue so far this year, a person briefed on the figure said. Executives have ratcheted back expectations for the business’ growth at least once in the past 18 months, two people familiar with the matter said.