I've done this groundside. Assuming you are not terribly out of shape and not huge bags, it is a pleasant walk, 15 min max. Probably less crowded at the departure level. I would do it over fooling around with the bus.
Be careful with pre-check in TBIT. Not all airlines do it. EI for example.

GE has been pretty instant for me in TBIT. The WN security lines a bit hit and miss though and Precheck Light seems to take forever. at off times.

The big risk is WN having a bad day - obviously things get worse as the day goes on usually.