With such a small playerbase, I think it's even more important to keep your players around, and not off doing other things when they log on the wrong alt or log on an alt that has absolutely nothing fun going on. I would be completely in support of lowering the switch time from 15 to 5. If I log on and I get the feeling that I really don't want to do whatever it is that particular alt is supposed to be doing and think statting a new one or levelling up that one I started not long ago would be more fun...and then I hit that 15 minute timer...I usually don't log back in. I have to find something to fill the time and then I generally get hooked on that.
As for using knowledge from one alt to another, we still have the knowledge whether we wait 5 minutes or 15. I don't really see why it's such a bad thing to be able to say hey, there's an awesome fight going on, I want to join in but I'm on an alt that can't fight others

, and then wait your five minutes and log on an alt that can and join in the fun, if it's even still going on. RP it as "oh I just woke to the sounds of battle! I should join in!" if you must. I haven't seen anyone on this game in my short playtime that has gone out of their way to be lame or ruin another persons fun. I think the majority of the players here are long time devotees and they should be given a break and some trust.