BIIP - Data Slices & Query Performance

Hello experts,

does anybody know the impact of data slices on query performance ? Or were we can measure the runtime of the data slices.

At the moment we use round about 15 data slices based on selection. Due to functional requirements it is not possible to reduce the number of data slices (when based on selection).

Can we improve performance by using 1 (or at least less than 15) data slice(s) based on exit class?

How is data slice based on selection working? Based on Exit, the Data Slice logic is processed for every record. Is it the same for data slices based on selection?

Thanks in advance

Johannes