1. I would certainly encourage you to try ndiswrapper. That's what I use (frankly, I was never able to get the 8187 driver to work correctly in SimplyMepis).
2. I can't imagine that "ndiswrapper" vs. "rtl8187 driver" could account for the "15 foot" limitation, however. Are you sure there's a clear line-of-sight? Does it happen with other OS's (e.g. Windows, or a different Linux?)
3. Could it be the router (for example, is it a Linksys router, or "something else"?)
4. Weird suggestion:
Try using a "Pringles" can over your antenna. No kidding - the aluminum cylinder (like an empty can of Pringles potato chips) can make a *great* booster. Try it - you might be pleasantly surprised.