Solution-
The C.P. of $15 \mathrm{~kg}$ of milk $=$ Rs. $7 \times 15=$ Rs. 105
To gain Rs. 64 ,
Total S.P. = Rs. $105+$ Rs. 64
= Rs. 169
Now there is $(15-2)=13 \mathrm{~kg}$ of milk
$\therefore$ The S.P. of $13 \mathrm{~kg}$ of milk
= Rs. 169
$\therefore$ Required S.P. = Rs. $169 \div 13$
= Rs. 13 ; Ans.