I don't judge it like pedophilia, there are many other teacher/student dramas too.
I have problem with reason - why he falls for her or she falls for him. Though this is really good, high quality drama, with amazing edit and cinematography, good acting and every reason to feel for characters, see chemistry, for me it's kind of misses something big/main from the beginning: ML is in love already in first ep, FL has feelings in 3rd ep, so soon we can't understand their reasons:

What he saw soo soon (almost without any interaction/communication), or what she saw while being in love with other and quite happy.
When you are getting married, really like/love your fiance, are happy and always smiling, there should be something really big to change it and start feeling for 15 year old (it's not only about taboo, but common things, understanding, which is more usual with same age people, and if there is big age/social gap there should be some big reasons, strong emotional changes, not only liking same poem, few meetings alone and hear "I love you" from teenager). Plus FL seems quite strong person, not usual naive/childish female from dramas, she knows what she wants, she really likes (I think loves, but I'm used to see in dramas when main lead then "discovers" that "it wasn't real love", because she/he was not main but second lead and real love should only be once in life and for main lead) her BF, so someone like her/in her situation there should be really big things to start changing feelings.

If they didn't rushed with main leads feelings, give them more time and reasons to see each other, feel, understand each other and then start loving, this would be perfect drama.