Doesn't make much sense to spend $22.50 for a test to tell you you've got another 3k miles left of service life. Not much of a savings over just changing the oil.
I can tell you that owning a BMW that was maintained under the "change it when the computer says so" (around 10-12k miles) method results in sludge build up. Not a schedule I recommend for something you want to keep long term.