What is a probable cause for this?

An international merchant is complaining that changes are taking too long to be reflected on the frontend after a full product import.

Thinking it may be database issues, the Adobe Commerce developer collects the following entity counts;

• Categories: 900

• Products: 300k

• Customers: 700k

• Customer groups: 106

• Orders :1600k

• Invoices: 500k

• Creditmemos: 50k

• Websites: 15

• Stores: 45

What is a probable cause for this?
A . The combination of the number of orders, customers, invoices and creditmemos is too big. This leads to a huge amount of values being stored in the customer grid index which is too large to be processed at a normal speed.
B . The combination of the number of products, customer groups and websites is too big. This leads to a huge amount of values being stored in the price index which is too large to be processed at a normal speed.
C . The combination of the number of products, categories and stores is too big. This leads to a huge amount of values being stored in the flat catalog indexes which are too large to be processed at a normal speed.