Realistically speaking it can't be done. You have a minimum of 4,000 miles round trip to cover in 15 days which works out to 288 miles per day and averaging 60 MPH overall that means driving 5 hours each and every one of those 15 days.
I would fly to Portland and rent an RV and do a loop through Idaho up to Glacier NP and back through Yakima, WA to Portland. Total distance covered of 1300 miles and less two days for air travel the 13 days works out to 100 miles per day to cover with the RV.
I have rented RV's in Calgary and Anchorage and the savings in fuel and food and hotels more than compensated for the RV rental and air fare. Net net we spent 10x as much time where we wanted to be rather than tooling down the interstate and dealing with traffic and truck stops and trying to find decent places to eat.