SE215 have more forward, lush mids, better bass overall IMO. The EPH is more neutral sounding, not as warm, more balanced across the spectrum. The treble on the EPH100 is technically superior and probably better in just about every way than that of the SE215. The EPH100 sounds clearer and cleaner, with better soundstage and instrument separation, whereas the SE215 sounds bigger, fuller, and more powerful; the overall sound is more forward but soundstage is not bad. The EPH100 is faster, notes are better defined, but the overall sound is smaller, a compromise between BA and dynamic sound; SE215 can be bloated sometimes and misses details, but it is definitely a dynamic sound and feels bigger and more powerful than the EPH100. There is more distance between the music and you in the EPH100, which helps with clarity and separation but sacrifices on the fun factor, which the SE215 definitely delivers, at the risk of sounding like a "wall of sound" sometimes. That said, the soundstage on the 215s is definitely better, especially in depth, than entry level IEMs like CX300 and FA Eterna (the Eterna wins on width but overall the staging feels less noticeable; going from memory on this one so take with a grain of salt), but is nothing to write home about; the EPH100 has great placement and separation, and has an overall more noticeable soundstage than any IEM I've heard, including the W3.
IMO:
Shure SE215 = more engaging, more fun to listen to
EPH100 = more detailed and clear, mostly balanced sound, technically superior headphone
Don't take this to mean the EPH100 is neutral compared to other phones; it's not exceptionally colored, but the bass is boosted slightly and it's a touch warm.
The SE215 does mids and bass both REALLY well in my opinion; I prefer it for my own tastes despite recognizing the EPH100 as a technically superior phone. The bass on the SE215 responds fabulously to EQ and some serious rumble can be squeezed out of it with the right DAP + EQ.
What music would you be using them for?