what you are looking for is hybrid mode which is not supported . Visuals can either access a dataset for which the data is stored in SPICE or dataset in direct query mode.
Below are the different scenarios
1/ Have 1st dataset with data stored in SPICE for visuals which do not require latest data.
2/ Have 2nd dataset in direct query mode for visuals which require latest data.
Note : A visual can access data only from 1 dataset .
If the 15 minutes refresh frequency works , have a look at the blog : Best practices for Amazon QuickSight SPICE and direct query mode | AWS Business Intelligence Blog
Kind regards,
Koushik