*read the whole thread*
The one thing that kept popping up in my mind was (since you said you two don't spend anytime alone since having the kids) asking a friend or family member to watch the kids for a night, rent a hotel room (before hand), take her out to dinner and then go back to the hotel and talk or have sex. Or even do something you guys did when you we're dating.
Second thing is what did you guys do about sex when you got married? I mean because you've been married for 15 years and that'd mean you'd be having sex for pleasure for around 9-10 years before she got pregnant with your first child, how did she see sex then?
Also I'd recommend going to a church counselor to talk about what's going on, if she really loves you, she'll want to work on making the marriage work.