diff --git a/src/main/scala/ninetyNineScalaProblems/Problem15.scala b/src/main/scala/ninetyNineScalaProblems/Problem15.scala
new file mode 100644
index 0000000..d3f8bcf
--- /dev/null
+++ b/src/main/scala/ninetyNineScalaProblems/Problem15.scala
@@ -0,0 +1,29 @@
+package ninetyNineScalaProblems
+
+import scala.annotation.tailrec
+
+object Problem15:
+    def fillList(value: Any, repititions: Int): List[Any] =
+        @tailrec
+        def loop(cursor: Int, acc: List[Any]): List[Any] =
+            cursor match
+                case c if c > 0 =>
+                    loop(cursor - 1, value :: acc)
+                case 0 =>
+                    acc
+
+        loop(repititions, List())
+
+    def duplicateElementsTimes(times: Int, list: List[Any]): List[Any] =
+        @tailrec
+        def loop(cursor: List[Any], acc: List[Any]): List[Any] =
+            cursor match
+            case e :: tail =>
+                loop(tail, fillList(e, times) ::: acc)
+            case Nil =>
+                acc
+
+        loop(list, List()).reverse
+
+    def duplicateElementsTimes2(times: Int, list: List[Any]): List[Any] =
+        list.flatMap(i => List.fill(times)(i))
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diff --git a/src/test/scala/ninetyNineScalaProblems/Problem15Suite.scala b/src/test/scala/ninetyNineScalaProblems/Problem15Suite.scala
new file mode 100644
index 0000000..42c33e6
--- /dev/null
+++ b/src/test/scala/ninetyNineScalaProblems/Problem15Suite.scala
@@ -0,0 +1,35 @@
+package ninetyNineScalaProblems
+
+import scala.compiletime.ops.boolean
+
+class Problem15Suite extends munit.FunSuite:
+    List(
+        ((0, List(1, 2, 3, 4)), List()),
+        ((1, List(1, 2, 3, 4)), List(1, 2, 3, 4)),
+        ((2, List(1, 2, 3, 4)), List(1, 1, 2, 2, 3, 3, 4, 4)),
+        ((3, List(1, 2, 3, 4)), List(1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 4, 4)),
+        ((0, List()), List()),
+        ((1, List()), List()),
+        ((2, List()), List()),
+        ((3, List()), List()),
+        ((0, List(1)), List()),
+        ((1, List(1)), List(1)),
+        ((2, List(1)), List(1, 1)),
+        ((3, List(1)), List(1, 1, 1)),
+    ).foreach:
+        case ((times, list), expected) =>
+            test(s"duplicateElementsTimes returns [$expected]"):
+                assertEquals(Problem15.duplicateElementsTimes(times, list), expected)
+                assertEquals(Problem15.duplicateElementsTimes2(times, list), expected)
+
+    List(
+        ((0, 1), List()),
+        ((0, 0), List()),
+        ((1, 1), List(1)),
+        ((1, 0), List(0)),
+        ((2, 1), List(1, 1)),
+        ((3, 1), List(1, 1, 1)),
+    ).foreach:
+        case ((repititions, value), expected) =>
+            test(s"fillList returns [$expected]"):
+                assertEquals(Problem15.fillList(value, repititions), expected)
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