Firstly I agree with the other posters about the guy already having run 5k and 10k races before. There are not many 1,500m runners who would find that session 'comfortable'
The predictive session for 5km is 4 x 1600m with 90 sec recovery. 1600 avge being the mile pace. This would give approx 14.30 for the 5km; double and add 1 for a 30min 10km
However, you supposedly did 2 more with 20 sec less recovery. So I would say 29.30
If you are right about feeling comfortable 29 is possible
Comfortable is a bit of a vague term though
What are you pr's?