This series is having 5 multiplication series . That is 5,1,5,5,2,10,5,3,15,5,4,20 so on .
Position of E is 5, J's position is 10 and whose one digit equivalent is 1+0=1 , E's position is 5 . Same way E's position is 5, next multiplication factor is 2 and K's position is 11 and the one digit equivalent is 1+1=2 , and 5X2=10 . DF's cumulative position value is 10 . Using same logic BC's total single digit position value is 5 , multiplication factor is 3 , AAA's total positional value is 3. hence Next number must be 15 .