How does Drupal 7 page/block cache work? I have a few questions about drupal 7 page/block cache.

If I enable the cache and set the expiration time for 15min., and the content in page A is updated within next 10min., will the cached version be updated? or will it only update every 15min.?

Does same apply to blocks?
From your question I get that you are trying to set the caching from the performance page admin/config/development/performance.

Cache pages for anonymous users only works for anonymous users, and the page markup is stored in database (to reduce the number of queries). And you can check the HTTP Header X-Drupal-Cache to see if this cache is HIT.

Cache blocks (if Page caching is disabled) works for anonymous and logged-in users. And again, the whole block markup is stored in database for the same reason.

Minimum cache lifetime is the amount of time before the Page cache gets cleared (the cache is cleared on cron run).

Expiration of cached pages works only if page caching is enabled and is only applied to external caching mechanisms (like the browser cache)