Hugo,

> Is it a good idea setting DefaultDbCachePages to high value like "15000"
> on a DB with page size 16k?

No.

With Classic you want to actually use a cache of 150-300 pages to reduce lock manager contention.

> The speed of my queries increases.

This is due to the huge page cache setting.

Remember to run queries a couple of time in order to exclude the cost/time of cache load when comparing results

> My question is about security. The environment is secure, nobreak, good
> server, hourly backup, etc.
>
> Could I have problems like data corruption?

In all other respects Classic engine functions the same as SuperServer