This is part of your problem!
You are using it at the highest setting! P = Power and 15W is far too high for stock atomizers. (6V is the highest voltage too)
I would suggest turning the dial down to 7W, start from there and increase the power little by little until you find a setting that you like.
However, whatever tank you are using probably has burnt coils now... The bad taste probably won't go away... you should replace the coil and/or look for a new/better tank...
As for the nic rush, as pointed out, I use 6mg and get a serious rush if using a dripper, and still quite a thump from a kayfun or fogger... but I also get a lot of vapor... On a smaller tank you can't get that kind of output so higher is good... As far as the 24mg, it's fine... at least for now... get your probably straight and you'll probably find out it's too much and you'll want to start bumping down, 18, 12, etc... but for now it's fine...
Once you get your settings dropped down, probably in the 8-10 watt range, and preferably new coils, if you want the maximum nic absorption with no "hacking fit" take a nice long draw into your MOUTH... Don't use your lungs to suck in, ONLY your mouth... Once the vapor is drawn into your mouth let it sit there a minute... take a moment to taste it... Then open your mouth and inhale it into your lungs... Then exhale it through your nose nice and slowly...
The molecules in vapor are much larger than smoke... It doesn't penetrate as deep into the lungs as smoke.... A lot of the nic is absorbed through the mouth and nose versus cigarettes where it's mostly absorbed in the lungs... So let it spend plenty of time in the mouth and nose... Believe me, get it right and that 24% will give you a serious head rush...
