WRONG.
http://science.education.nih.gov/supplements/nih2/addiction/images/guide/fig3.6.gif
http://science.education.nih.gov/supplements/nih2/addiction/guide/lesson3-1.htm
"A drug that is inhaled (smoked) reaches the brain very quickly. The inhaled drugs go directly from the lungs into the left side of the heart, where they enter the arterial circulation that carries them to the brain. Marijuana and nicotine are examples of drugs that are commonly taken into the body by inhalation (smoking). The intensity of the effect of inhaled drugs may be slightly less than that for injected drugs because less of the drug is taken into the body; some of the drug will be exhaled with the rest of the components of the smoke. A drug that is injected intravenously also travels quickly to the brain, where it can exert its effects. The rapid passage of injected heroin, for example, brings a high risk of overdose."
15 to 20 seconds to feel a hit of inhaled meth? Try 2 seconds. IV rushes are more overpowering once they hit you from what I have heard (and seen, although not with heroin so none of them passed out), but not as immediate and not as steep or choppy.