Basic strategy says to double a soft 15 vs a 4, but hit a soft 14 vs a 4. With both those hands there are five cards that can get you to 17-21.

Not doubling a soft 15 you need an ace in order to be under soft 17. With a soft 14 it’s a 2 or an ace to be under soft 17.

The only advantage I see to not doubling a soft 14 is you can catch a 2 and rehit the soft hand.

The risk seems exactly the same as there are the same amount of cards available that can help you make an actual hand. Why not double this?

You’ve done pretty good calculation there. I never think so deep and maybe that’s the reason I don’t win too often.