The specs other than cassette and chain don't matter in this case, and even those are not that important in this case - it's a generic problem. There's no standard time before something fails varies too much depending on usage, conditions and luck. After 2 years you certainly should check the chain for wear (Sheldon's or Park tool sites give instructions or someone can post them here for the 1000th time. If the pedals go around only under pressure it probably is the chain/cassette. If it happens when not under pressure, and especially if it happens more often when not under high pressure it's probably the freehub.