I gotta admit I laughed when I saw that.

Hey plx! If the pedals make you faster at all, the speed difference will be negligible. They definitely won't make you get tired faster unless you do something strange. The reason you're slow now is that both your conditioning and your form need a lot of work. Clipless pedals could encourage proper form and if they make riding more fun that would help your conditioning, so indirectly they might speed you up. Don't expect any miracles though.

There is a reason why the vast majority of experienced cyclists use clipless pedals, so I'm definitely support getting them if you are interested in them.