What is Considered Too Big for Virtualization?

A customer recently asked me, can we virtualize our Tier 1 App that receives 7Billion requests per day? My initial response was, on how many servers? Their answer was 15. This is quite a shocking set of numbers to consider. Add into this numbers such as 150K sessions per second, the need for a firewall, and sub-second response time and you end up with a few more shocking numbers. So could such workloads be virtualized? or is it too big for Virtualization?