need help in tuning this process

Hi All, 

we have a process which is suddenly taking long time to execute,we found that some of the deletes/inserts are taking longer to run. below Delete is taking  about 3 mins  and the Insert taking about 6 mins to process 300k rows. these Delete/Insert stmts gets executed once for each process group, and we have 300+ such groups processed in the schedule run of this process. Many of these Delete/Insert stmts fly in very few seconds, but if the data is more than 150k rows to Delete/Insert then those appears to be taking longer to run. 

Out of total 300+ process groups, we have about 30 such groups process above 150k rows. Is there way to make these deletes/inserts faster?