Hi scall,
15psi is about spot on for a Badger 100.
I've never airbrushed Vallejo, so unfortunately i can't comment on ratios, but when i use Gunze or Tamiya acrylics, i thin about 2:1 paint to thinner. If i want to do detail work, i'll go about 1:1 and reduce psi to about 10.
Also, if you're getting pooling, there is way to much paint hitting the model. You could:
1. shoot from further away (the issue that the paint is "too wet", as you've described, may be reduced by this), also, you'll get better coverage over larger areas;
2. reduce how much you open up the needle. ie, the 100 being a dual action, don't pull the trigger all the way back, otherwise you're blasting as much paint as possible through the tip. Just pull back 1/5 or 1/4 and see how you go.
Above all, don't give up and keep practicing!