If the site takes twenty seconds on a D525, it's probably pretty demanding server-side and will require solid hardware to deliver many requests at good performance. Imagine if you're using a machine twenty times faster than the D525 (i.e. a modern desktop CPU), assuming linear speedup you can generate the page in one second. That's one second per pageload per user, and that modern machine is going to likely choke up too if the site gets decent traffic.