Childhood amnesia refers to the phenomenon where adults often have difficulty recalling specific details about their early childhood years, typically up until around age 3-4. This is not due to any traumatic event or repressed memory but rather the natural process of brain development and maturation. As children's brains continue to develop, older memories are gradually replaced by new ones, making it more challenging for adults to recall specific details from their early childhood.

Repression, on the other hand, is a psychological defense mechanism that helps individuals cope with overwhelming or traumatic experiences. When faced with an emotionally distressing event, the brain may temporarily suppress the memory to avoid further emotional pain. However, this repression is not a permanent erasure of memories; rather, it's a temporary avoidance mechanism.

In the scenario presented, it's possible that the individual experienced a traumatic event around age 15 and repressed their memories to cope with the emotional distress. This could have resulted in a gradual loss of recall for events prior to the traumatic experience due to normal memory decay or interference from subsequent experiences. However, it's unlikely that this would result in a complete erasure of all memories prior to age 15.

Other factors may contribute to the individual's perception of erased memories, such as:

1. Confabulation: The tendency for people to fill gaps in their memory with false information, which can create the illusion of lost memories.

2. Misattribution: Memories from around age 15 may be mistakenly attributed to earlier times due to the influence of subsequent experiences or emotions.

3. Social and cultural influences: Societal norms, cultural practices, and personal beliefs can shape an individual's perception of their past, leading them to believe they have forgotten certain events.

To better understand this scenario, it would be essential to gather more information about the individual's traumatic experience, their current emotional state, and any potential psychological or neurological factors that may be influencing their memory. A thorough examination of their memories and experiences, potentially using techniques like cognitive interviewing or brain imaging, could help uncover the underlying mechanisms driving their perception of erased memories.

In conclusion, while traumatic events can certainly impact memory, the idea that such an event would erase all memories prior to age 15 is unlikely. It's essential to consider the complex interplay between childhood amnesia, repression, and other psychological and neurological factors when exploring this scenario.