The air in the Woodvil bottle is at the top of the bottle and the tube opening is at the bottom of the bottle with the juice. Since the outside air pressure reduces as you climb, the air pressure at the top of bottle increases relative to the outside air pressure, since the air pressure in the bottle has no place to go, it exerts downward pressure on the juice, thus the juice is forced up the tube. It's the same as squonking. The juice does not expand and cannot be compressed (except under great pressure), so when we squonk, we increase the air pressure in the bottle, which increases the pressure on the juice and forces it up the tube.
With increased air pressure in the bottle, the plastic bottle itself will expand a small amount and 1500 feet is probably within the limit of that expansion and shouldn't cause auto-feeding. However, if the juice is near empty, which means the bottle is almost full of air, then all that air will expand and most likely cause auto-feeding.
If the cap on the bottle is loosened just enough to let the increased air pressure in the bottle escape, then the inside and outside air pressure will equalize and all will be well. However, it may not squonk very well with the cap loose.
There is a consensus among REO owners that as the juice is used up, it becomes more difficult to squonk. That's true, because the air in the bottle increases and that air has to be compressed enough before the pressure on the juice is sufficient to force it up the tube. That is why going to a larger 10ml or 12ml bottle may not work well for our arthritic friends. The pressure exerted as the juice level decreases and the air volume increases may be too much for some folks. That's why I feel the future for bottom feeders will be automatic squonking.
I hope I explained clear enough your thoughts and questions.