\def\Bla{\dorecurse{12}{bla }}
\def\Section#1{%
 \startsection[title=Title]
   \dorecurse{#1}{\Bla}
 \stopsection}
\starttext
\startmixedcolumns[n=2]
\Section{15}
\startsection[title=Title]
  \dorecurse{10}{\Bla}
  \footnote{\Bla\Bla}
\stopsection
\Section{9}
\Section{9}
\Section{2}
\stopmixedcolumns
\stoptext