Channel listings can take a lot of time on large networks that have tens-of-thousands of channels. Sometimes you can speed things up by limiting the response of the LIST command to only return channels with 10 or more, or 30 or more users. ie, /LIST >9 or /LIST >29 *searchwords*
Most servers do not allow you to interrupt a LIST command. You just have to sit and wait it out. It can take a couple of minutes. Some servers artificially slow down the output of LIST to prevent network abuse and discourage frequent use. Some networks will encourage you to use a channel listing service bot, ie, /msg Alis HELP LIST
Generally speaking, entirely 90% of channels on large networks will have fewer than 10 users. 95% have less than 30 users, which is usually the size of a reasonably active/public channel.