Is it allowed to do BA(economics) from IGNOU and do 3 yrs course LLB from ILS,Pune instead of doing 5 yrs course. So that, i can save 2 yrs

If you are graduate and your age is less than 30 years upto the 1st July of the year your are interested to be admitted then only you can go for 3 years LLB Course. Otherwise you can go for a 5 years course if you are a 10+2 pass out and your age is not more than 20 years upto 1st July of the year y

For LLB (3 year course) its necessary to have a bachelor's degree passed with atleast minimum marks. One cannot pursue LLB 3 year alongwith Graduation. So you'll have to complete atleast your second year BA and apply for LLB with the "Final year result awaited".

if you want to do at same time then you have to do one course through distance mode

Graduation from IGNOU is a valid degree and enables you to pursue a Three Year Law Degree.