If possible, run a quick stress test for your own peace of mind.

For example, you could run a test where you tie many DB_Files (i.e. much greater than 8) and randomly add/remove many records (i.e. much greater than 15000) to each one. While this is running, watch the resources used (CPU and disk utilization, etc.).

If you know DB_File performs ok under worse conditions than you expect, it will probably be a good indicator on how it will perform under expected conditions. If it doesn't perform well, you can cut back the numbers until you find out what its limits are and then plan to redesign your program accordingly.