You're in the right place. I assume that your meeting will be near Facotria where 90 and 405 intersect. Is that correct? If so then in normal non-peak (Saturday midday) times it should be 15 minutes to the City of Sea-Tac. 5 more to get into the garage though. At 1600 it is before rush hour so maybe 30 minutes down to SEA. You miss "Downton" Bellevue so no need to worry about that traffic which I need to worry about going to SEA. Just wondering, why the 1715 time requirement? What time is your flight?

Assume 45 minutes for security/boarding if not checking bags (5 extra minutes for the satilites, INTL/NW/UA/AC/some AS)
15 minutes for returning rental car/to security if already checked in
X for driving
Your flight time-1 hour minimum+4 hours=time you have to drive.

If you are not checked in online and are not checking bags utilize the easy check-ins placed in the terminal to the right or left at the end of the skybridge on the landing (You'll know it when you see it). Much quicker than normal lines.