How long do you mean by slow. If you have a few good links from other sites to yours you should get indexed a week or so.
How long does it take? Week or Month? If you have quality and high authority one way links(i.e wikipedia,digg, Flickr) then process make fast.
Well, it is never enough for a new site to get indexed relying merely on a sitemap. You have to build quality backlinks to help you.