15.4 does not directly required the serverless but for fine-grained it indeed requires it to run it on Single User as mentioned
This data filtering is performed behind the scenes using serverless compute.
In terms of costs:
Customers are charged for the serverless compute resources that are used to perform data filtering operations. For pricing information, see Platform Tiers and Add-Ons.If you dont want to enable Serverless on this case you will need to continue using shared access mode, which the main implication is that multiple users will be able to use this cluster if they have permissions to.
