dude, nice jumping! you've made MUCH improvement since that 2 1/2 year-old video. If you notice, your pole on the 15'3 make sags a lot and spits you off the top, where as in the 13'6 and 14'6 makes, the top of the pole RISES which is great. It's better on the 13'6 make than the 14'6 make, but it's still improvement from the older film. Anyways, if I was your coach, I'd have you try to get your stop out (free) and then attempt to keep my trail-leg straight throughout the jump. I'll explain the first part before the second...
The Swing: in your case, you swing to about the chord of the pole (the point at which your toes are pointing at the lower half of the pole), and then you pick your feet up into a tuck. I understand why you tuck (your take-off, which we'll get to in a second) and you've probably been taught to tuck. When you tuck, you stop putting energy into the pole and in turn it will start to unbend. Unfortunately, it unbends before you can finish inversion and you therefore have to struggle and tuck to invert; which also lead to you being at an angle (flagging out), instead of completely perpendicular with the ground, when the pole is completely unbent. Now, if you were to swing all the way to inversion (keeping your trail-leg straight during the entire duration of the vault) you'd continuously put energy into the system and by the time the pole began to unbend, your hips would already be above your shoulders and you be in a better position to 'pop' off the top of the pole. In addition, since you don't stop putting energy into the system (as you would with a tuck) you can get on bigger poles and your push-off could go from 26" to 36" pretty quickly.
Take-Off: it's not bad but you're definitely under and this prohibits you from being at a proper angle at take-off and therefore lessens the power you can put into the jump with your speed and your swing. Now, ideally, you'd like your toe to be just leaving the ground before the pole-tip hits the back of the box (free). Because your whole foot is on the ground, now the pole is pushing back at you and slowing your down. If your take-off was free, ALL of your speed from your run would go into the vault, not just he leftovers. Because you're taking off under, your not able to "lean" forwards the way you would like to and that means your trail-leg isn't really behind you to whip forward as powerfully as we'd like. So that's a pretty big thing to work on.
I'd fix the take-off FIRST because it's easier to swing once the take-off is out. Many elite vaulters tuck because they take off under. Bubka and Tarasov swung very well because they both had free take-off which allowed many other good things to happen during the jump. You're looking good buddy and with a 26" push-off you'd be surprised what that can turn into. A great coach once told me that if you can push over two feet, than you definitely should be gripping over 14'6. Once you fix the take-off and swing, you can start upping the grip (while making sure you don't develop a sag in the pole like you used to) and if you can still push 26" - 28" with a 14'4 - 14'6 grip, well that's 16'. Think on that
-6P