The service interval is, and I repeat, UP TO 15,000 miles or 12 months.
If you hit 12 months, with 2000 miles on it, thats time for it to be brought in. A modern car should be inspected thoroughly by a qualified mechanic every 12 months or so, regardless of any other needs, and changing your oil and filter is not a bad idea, either. Not every safety issue, mechanical problem, or impending failure can be detectable from behind the wheel, or from outside the car.
Furthermore, if you drive it in less ideal conditions, such as in frequent stop and go traffic, around town driving, lots of rapid accelerative events, hard braking events, cold starts, or very hot days, your car will reduce that interval. As it should. The idea behind ASSYST is to eliminate unneeded servicing, and keep the car on the road and out of the garage as much as safely and intelligently possible, without reducing ultimate service life or safety. A person who drives their car 40,000 miles a year and spends a lot of it on long highway trips out of stop and go traffic has no need to service the car more than 15k miles, which is inherently a lot less than 12 months. Thats me, by the way. *waves*
Its a lot better than the old 6mo/7500 mile intervals they had before ASSYST, which were not much cheaper inflation adjusted, by the by. American and to a slightly lesser extent, Japanese, cars are built for US consumption with certain things in mind, one of which is that Americans do not know how to maintain cars. They use less precise assembly and more forgiving but less ultimately durable design to compensate for the fact that they will generally remain unserviced and unmaintained except for the oil change, which is actually with todays oils one of the least important parts of car maintenance.
European cars in this country, with the possible exceptions of VWs Jetta and Passat, are not designed for that market reality, for better or worse. Mercedes automobiles are designed for owners that maintain them religiously. Europeans treat their cars as more valuable possessions than Americans do, and European inspections are strident, strict, thorough, and in many cases are done more than yearly. If you bought a Mercedes, it would behoove you to not neglect maintenance on it according to schedule, and to do it either at a dealer, or at a garage that specializes in Mercedes or at least European brands. They are easy to spot, because there is generally a fleet of older European cars perpetually littering the property- if they don't have that, don't use them.
Properly maintained, (which is not cheap) you will love your Mercedes Metris and it will last you for longer than you'd imagine. If you fail to do this, you have bought a money pit that will cause you no end of aggravation as all kinds of things break because the required inspections and related adjustments are not done, and parts that are approaching the need for replacement are not caught in time and will take other components with them when they go, and so on.
If you are not willing to service the car when it tells you to do so, let me give you the best advice you are ever going to get on the subject: Sell it and buy a Ford Transit.