15 year old McDonald's toys aren't worth too much. In fact, McDonald's toys from around 1985 are selling on eBay for approximately $4. It's unlikely that there's much of a market for old McDonald's toys, but if you have a lot of them you might be able to make a little bit of cash.
History of McDonald's toys
These days, toys are given out as part of a Happy Meal, but they have changed dramatically over the years. Initially they were very simple plastics toys, but with sponsorship from Disney, the toys became higher quality. Disney don't actually associate with McDonald's anymore, however, as they don't want to be seen to be associated with unhealthy food.