Complex sentence: But in 1975, he moved from Cambodia when he was 15 years old to Udon Thani, Thailand, then 5 years later, in 1980 he fled to Hong Kong in where he took a job as a tour guide.
Split into simpler sentences: But in 1975, he moved from Cambodia when he was 15 years old, and then to Udon Thani, Thailand. Then 5 years later, in 1980 he fled to Hong Kong in where he took a job as a tour guide.