Business advisers BDO found occupancy rates dipped by 0.9%, while rooms yield fell by 2.2%.
This compared with increases in both categories in regional UK, England and Wales.
BDO said a poor year for Aberdeen hotels had "skewed" the overall performance north of the border.
Average rooms yield in the Granite City fell last year by 22%, from £68.71 to £53.60, while occupancy was down by nearly a fifth, from 78.5% to 64%.
However, other cities performed strongly, with Edinburgh recording the fifth highest revenue of any city outside London.
Glasgow had the third highest occupancy figure outside London, after Chester and Southampton.
In Inverness, revenue was up 4.3% to £55.26, while occupancy fell 1.7% to 80.5%.
Alastair Rae, from BDO, said: "Scotland's hospitality sector had a pretty good year in 2015 with the exception of Aberdeen, and it is that city's figures which have skewed the overall performance of the hotel industry in these numbers.
"But, although the fall in occupancy and revenue in Aberdeen is severe it is partially because it was from such a great height.
"Despite a 22% revenue fall year on year Aberdeen still has a higher figure at £53.60 than Glasgow at £51.82. This reflects the very rarefied market that Aberdeen occupied prior to the fall in the oil price."
He added: "There are signs of some stabilising in the oil price so I would expect the downward curve in the occupancy and revenue in Aberdeen to reduce somewhat as the market comes to terms with its new operating environment.
"Across the wider market I would expect the coming year to be slightly better but not exceptionally so."
Scotland's hotel sector had a "pretty good year" in 2015 despite an overall fall in occupancy and revenue, according to a report.