What must you do within 15 days after changing your name or address?

Answer: B — Advise SGI in writing

After changing your name or address, it is important to notify SGI in writing within 15 days. This option is correct because it is a legal requirement in most places to update personal information with relevant authorities, and this includes your name and address with SGI. Option A (notifying your employer) is incorrect because it is not a legal requirement and your employer does not require this information for their records. Option C (updating your vehicle registration) is incorrect because although it is important to update your personal information with SGI, it must be done in writing and not through updating your vehicle registration. Option D (retaking the driving test) is incorrect because changing your name or address does not affect your driving ability and therefore does not require a retaking of the driving test.