\vspace if used mid paragraph, as here, stores the vertical space in a special place (a vadjust node) which is then inserted after the paragraph has been broken into lines, after the line on which the space is added. in your example the \vspace is added in the last line of the paragraph so the space comes after the paragraph. Compare
\documentclass{article}
\begin{document}
\noindent
Hallo \\
How \\
Are \\
You?
xxxxx
\noindent
Hallo \\
How \\
Are \\
\vspace{15cm}You?
xxxxx
\end{document}
to add a space at the linebreak you should use
\\[3cm]
but it is almost always wrong to use \\ at all apart from its use in tables.
In cases like this, I write
a lot of stuff I write\\
a new line\\
\vspace{15cm} \ \\ % the \ is necessary, otherwise you will get a no-line-to-end-error.
You
\vspace and \hspace are very sensitive to new lines (\\) and new paragraphs (double linefeed). Changing vspace to \vspace* is also always a good first try.
There will be people saying, that this code isn't beautiful. Remember: All codes are beautiful.
Areand remove the\\\– Apr 01 '16 at 13:21\\[15cm], but you're misusing the tool anyway. There is *very rarely* need for\\in normal text. – egreg Apr 01 '16 at 13:23\parinstead of\\\after "Are". – A Feldman Apr 01 '16 at 13:25