From the information you provided, I’d say that those are simple queries (fast to execute in the RDBMS), that return many rows (slow to de/serialize in the backend and transfer).
If the current performance is blocking your use case, there are many different solutions you can explore:
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Lowering row counts per page, so each page is faster.
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Building a plugin that exposes the same information in a new API endpoint and is smarter about caching and data format.
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Querying the underlying database directly.