For the first week, they bought 10 + 5 = <<10+5=15>>15kgs.
For the next week, they bought twice the quantity of oranges which is 2*15 = <<2*15=30>>30kgs.
For the next two weeks, the total quantity of oranges bought is 30*2 = <<30*2=60>>60 kgs.
The total quantity for the three weeks is 60+15=<<60+15=75>>75 kgs
#### 75