Amplifier question

Hello, i have this amp http://store3.sure-electronics.com/2-x-15-watt-class-d-audio-amplifier-board-ta2024 and it says that it gives 15w*2 channels. If i use only one of the channels (since i now have 2 60w 4ohm speakers hooked to it and it takes a lot of space) would sound loudness suffer? As far as i understand, there shouldn't be any difference between 2 speakers running 15w each, and just 1 speaker. Since they both run 15w individually. So, would using only 1 speaker, only 1 channel of this amp, cut some of the loudness?

P.S sorry if it's a dumb question, i don't understand how dumb can it actually be because i have no experiece with amps and so on...