I have a 2002 QX4 and just finished an Auto-Rx cycle. I normally go 7,500 miles between changes on Mobil 1 5W-30 or, more recently, Shell Rotella T 5W-40. Aside from an intake leak I'm trying to seal, the oils have been in fine shape, even after a year of service.
So, my point is that, assuming you have no mechanical issues (fuel dilution, coolant leaks, etc.) and that the current fill is a reputable oil, you can easily add the Auto-Rx to your current fill, change the oil filter, and drive an additional 1,500 miles without danger.
Of course, a good inexpensive 5W-30 oil like Chevron Supreme/Havoline isn't much more than a buck a quart, so it wouldn't hurt to do an oil and filter change and run the Auto-Rx for 1,500 miles, either. This is probably the safest plan, especially if you aren't 100% sure that the engine is without issue.