How much SPAM do rest of you get.

I am a network admin for small to medium based company with over 150 users. Recently users started complaining more about daily SPAM they receive and that prompted me how much spam rest of the orgnizations get. We use GFI products and according to reports it catches about 90% of SPAM rest does trickle through but across 150 users its less than 15 for heavy users. I was also doing some reports on the server and noticed since our upgrade we received over $100k emails is that normal amount or is there something else we can do to reduce the number. Any thoughts suggesstions are more than welcome.