Hello Bala,
my suggestion would be :
1) create secondary index on vbak based on fields VBELN , lifsp , edatu and bmeng in SE11.
2) optimize your select query by using basic thing, like dont use select * , dont use into corresponding table of fields etc.
3) make use of abap trace is possible, to cehck which statement taken how much time (in micro seconds)
Regards,
Hitesh