If you think about it, there's not really a "quarter 'till" here technically. It's still "fifteen minutes" and so if you are saying it's 4:15, then why add another word on the time if already you have stated the fifteen minutes? I don't know of an equivalent specifically to the word "quarter" in Japanese, especially pertaining to time. That's why there would be no equivalent, like say: 四時十五分後 「よじじゅうごふんあと」 because after the 分 「ふん」 we've already stated it. I think I just overstated myself.. :( I'm sorry.. I'm bored, lol.