We have an ongoing discussion here.
https://wordpress.org/support/topic/too-many-wc-transients-created-in-db?replies=40
If you read a bit then you see that my splendid mate Mike Jolley is aware of the problem and has implemented a possible solution for this in WooCommerce 2.5 – fingers crossed
But you do not need to wait that long.
You can try and tackle this manually using this:
plugin: https://wordpress.org/plugins/delete-expired-transients/
plugin: https://wordpress.org/plugins/transients-manager/
plugin: https://wordpress.org/plugins/artiss-transient-cleaner/
Using our tools will also alleviate the issue.