With all due respect, if there is any, krillco's answer is probably the most asinine thing I've ever heard in response to a situation such as yours. Verbal abuse, threats, and constant arguing definitely don't mean that things are going "right" with your marriage and to say so clearly tells that krillco knows nothing about relationships (so I'd avoid any links he/she tries to direct you to that were authored by him/her).
Arguing? Threatening to possibly leave you? Belittling you regarding your opinions and feelings (which IS verbal abuse)? Everything you say causes him to be angry?
First of all, he is deflecting, is in denial, and is transferring. He CHOOSES to be angry over things you say because of something that is a problem with HIM, not with you. He thinks you shouldn't be together? Does he act suspiciously or give you any reason to think he's cheating on you? Usually, when someone wants "time to think" or wants some "personal space" or is considering ending a relationship, they've found someone they are "more interested" in, at least on the surface. They think the grass is greener on the other side of the fence.
He feels neglected, according to you. Have you asked him to be more specific about what, exactly, he feels neglected about? Not enough sex? Not enough personal attention? You spend too much time working? You don't clean enough, cook enough, wash enough clothes? You need to find out - from him - what his specific area of neglect, in his mind, is...and then address that.
Conversely, considering the things you've said, the relationship could have reached a point where he doesn't feel like he wants to invest any more time and attention to it...even after 15 years of marriage. People DO "fall out of love" with their partners occasionally, but when this happens, it usually means they weren't really "in love" in the first place.