Oh boy another oil thread. Well here goes, I purchased my e46 brand new and followed 15k oil changes without any problems (sludge) after 180,000 miles. I gave the car as a gift to my bro-in-law and it is still purring after 190,000 miles. Since finding the OP's other crazy posts, I don't think this thread is a definitive answer to not follow BMW's recommended interval. On my e90 I change oil at 10,000 miles for the heck of it.
Also, keep in mind, if 15k oil changes were unrealistic and produced sludge, there would be thousands of posts/complaints coming from e46 owners. The e46 has been in production for about 11 years now. Also, someone (like the OP,
) would have filed a class action lawsuit by now.