Is it possible to merge quizzes?

Yes, merging quizzes is available through the "Import" function. To merge two quizzes, just open one of the quizzes
and press "Import" on the ribbon. In the "Import" window that will appear, locate the second quiz and press "Open".

Merge several Flash quizzes

All the questions from the imported quiz will appear in the list of questions of the currently opened quiz.