i understand about rev matching and going through gears in sequence...but if im going under 20mph in 4th if i shift it into 3rd i'd be in too low of a gear. So would I still shift into 3rd then shift into 2nd instead of just clutch in, neutral, 2nd?

 

just be in the right gear to keep your rpm's above 3k if possible. In your scenario of being in 4th gear and slowing to 15mph it is the right thing to do to shift down to 2nd gear. If you tried third at that speed your rpm's would be way to low, and depending on how much throttle you used you would have a strong chance at lugging the engine.