Don't know that this is the correct answer, JGA....but here's my best attempt :
If we have 10 ditinct positive integers....the median is the average of the 5th and 6th data values [ assuming the we have ordered the values in increasing order from left to right ]
It's obvious that the first four integers will be 1, 2, 3 , 4
To have the smallest overall average, we need to have the 5th and 6th values as close to 10 as possible such that their average is 10.....these are 9 and 11
And the remaining integers are 12, 13, 14 and 15
So....the data set is
1,2, 3, 4, 9, 11, 12, 13, 14, 15
The median = 10
The average = 8.4