It is possible with no hiccups whatsoever as the traffic may take 75 minutes. Traffic in LI is bad but nothing in comparison to California as there are three parallel highways to head east.

Adding complex components (which make it more challenging):
Does your flight land ontime? (i.e. bad weather)?
Does your flight get to the gate quickly?
Do you have check baggage and have to wait for it? Are you priority on airline or sitting in the rear of a jumbo jet?
Are you an elite member at rental agency (grab and go) or have to wait in line?

Each item above can easily add 15-30 minutes resulting in a 5pm landing turning into a 6:20pm exit from airport.

My suggestion to avoid stress/panic -
-take earlier flight arriving at 3:30pm. No rushing and sleep on plane.
-If the earlier flight is not an option - instead of rental car hire a private car service to handle your driving and meet you at terminal as they will know alternate roads (traffic reports, etc.) and save you on time to pick up rental car. You can take train service back to airport from Port Jefferson and avoid driving altogether if possible.