The process of retrieving a page from the Internet is not slowed by using a proxy except when the requested page cannot be retrieved. In this case, the proxy will try for up to 2 minutes (120 seconds) by default to try to retrieve the page.
This can be annoying to the user, and will certainly have users knocking on your mailbox complaining.
One means of speeding this up is to change the connect_timeout time. If you make this too short of course, the page will never be retrieved since the latency on the Internet may well be significantly slower than 20 seconds (although I would look at my Internet access connection if this was the case!).
I have changed my connect_timeout to 20 seconds and one means of testing this is by issuing the following commands:
date +"%s";lynx www.nowhere.biz
Compare the time in the access.log file for the www.nowhere.biz entry to that on the command line as output by the date command.
Since squid prints the times in UNIX formatted time (i.e. Number of seconds since 1/1/1970), it will be easy to subtract the time as displayed by 'date' from the time in the access.log file and this should show you the connect_timeout.