[Modify/Add] Improved practice exam layout and turned it into an interactive test experience.

practice-exam/practice-exam-15.md

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-# Practice Exam 15
-
-Click on the **Answer** button for the correct answer and its explanation.
-
-If this practice exam has been helpful to you please share it with others and react to this below.
-
 ---
+layout: exam
+---
+
+# Practice Exam 15
 
 1. How do customers benefit from Amazon's massive economies of scale?
     - A. Periodic price reductions as the result of Amazon's operational efficiencies
@@ -886,6 +884,3 @@ If this practice exam has been helpful to you please share it with others and re
     Reference: <https://cloudranger.com/best-practices-aws-disaster-recovery-planning/>
     </details>
 
-Please feel free to comment below if any information is inaccurate or if any answers need correction.
-
-[<img align="center" src="../images/list.png" height="30" width="30"/> Exam List](../practice-exam/exams.md)