I only ride a little less than half your distance and even so I'm a fervant clipless fan even over that distance. I've got a couple of bikes I also use without clipless and while I like them for what they are (MTB's with pinned platforms so I can play a bit on the commute) they are not as "efficient" as the bikes with clipless. Compared to the clipless where my foot position is set by the clipping in the platforms require a LOT more fussing around to get comfy positioning and then it's time to lift my foot off again. Non pinned platform pedals would get away from that issue but then my feet would tend to slide around and I'd STILL be constantly altering them. So clipless it is for me.....
For commuting I'd have to say ditch the one sided pedals and do NOT replace them with the one side clipless and one side platform. Get the MTB double sided clipless in some format.
Why? Glad you asked...
In commuting you're in and out a lot thanks to cross streets and lights. The double sided MTB clipless means it's a full on no brainer for clipping back in sinde you never need to worry about being upside down and flipping to get in. The MTB double sided style lets you just jam your foot down and the pedal flips if it's edge on and you have an open trap waiting for the cleat. Makes for real easy clip ins.
Riding clipless DOES mean you need a change of shoes at the other end. But over a 15 mile commute you'll want to change clothes at the end anyhow. So I'm guessing you have a locker or other area to ditch the riding gear in while at class.