Congrats on the 15 lb loss. But at 5'7", 167 lbs is still fat on a female. Even if you were slightly muscular, roughly 130 lbs would probably be perfect at that height. With that being said, I bet you've got at least 30 lbs to drop before you can even hope to have the flat belly you want.
If you've already lost 15 lbs and fat loss hasn't stalled, it sounds to me like everything you are doing is perfect and you aren't making any mistakes at all. You really just need to be a little more realistic and a lot more patient. When all your fat comes off, your belly fat will come off along with it.
Keep doing what you've been doing that's been working and don't change a thing. Have some patience and you will get to where you want to be.
As for the coffee, so far it hasn't seemed to have stalled your progress because you already lost plenty of weight. I don't know of any studies showing it's affect good or bad on fat loss. However, it is an appetite suppressant, and that's a good thing for fat loss. Regardless, the calorie deficit is what is required for fat loss and such should be natural with or without coffee.
Aside from that, caffeine causes anxiety. I recommend staying off it completely if you can. I gave it up completely and don't regret it a bit. I'm much more happy, relaxed, and stress free.