i'm on many channels and therefore i use up about 2 to 3 lines for everything there is, most of the time having 4 lines max activated.
(yes, on some channels its just me and some very few other people and on some its just me and myself, but thats not the matter.. -.-)
but the channels just wouldnt fit all into the lines at once anyways, so i hide several channels using "window -hx" which stay hidden until either something happens in general in that channel or until someone highlights me. so i'm still in these chans, ppl can reach me if they need to and i dont loose overview.
15 lines wouldnt be much of a problem though on 1600x1200 and higher resolutions. still looks silly somehow ..