For the bigger tables inside SSISDB I have executed the below procedure (just replace the table name) to see what was the expected results:
@schema_name = '',
@object_name = 'TransactionHistory',
@index_id = 2,
@partition_number = NULL,
@data_compression = 'PAGE' ;
This will show you what do you have to benefit from doing data compression. Then, for all the tables that have big advantages and because SSIDB is a database with not much updates, you can do the page compression to gain space and to get your i/O and disk latency better.
Hope this helps.