According to the handbook (p.479 in the version I'm looking at, may be different page in yours), the change interval for the fluid in the manual box is every 72,000 miles or 6 years for "normal use". The Mk.3 only became available in UK in mid-late 2015, so only high-mileage users are likely to have reached this milestone yet. 2.5 years does sound a bit early, unless your car has had a particularly hard life so far.