I'm new here, but I make sourdough bread for my restaurant on a semiweekly basis. Spelt is just an older variety of wheat, and makes great bread. If your dough is wet, that's good. Wet dough makes for a better loaf, generally, even though it's difficult to work with. After fifteen minutes of kneading, was it still super sticky? Or just tacky? Was it smooth?
Regardless of how long you kneaded the bread, you want to knead until the dough had developed enough gluten to pass what's called the "windowpane" test: Pinch off a golfball sized hunk of your kneaded dough and round it. Press the center of the ball with your thumbs and fingertips, thinning it somewhat, and then stretch it. You should be able to stretch the dough for quite a distance before it breaks. In fact, it should be so thin and transperent, that it will look like a dough "window." http://www.wildyeastblog.com/2007/07/07/gluten/
It may also help with the stickiness (and gluten development) to let the flour soak in the liquid for fifteen to twenty minutes before you add the sourdough starter and salt.
Another way to maximize lift in the dough is to put the dough, when ready to bake, in a super hot oven (450 F. or better), and then to steam the oven (throw a handful of ice cubes, or a cup of ice cubes in about a half-cup of water into the oven, after the dough goes in, being careful to minimize any heat loss by working quickly to shut the oven door as soon as possible). After about ten minutes, you could lower the heat to 400 or whatever you'd bake the bread at normally.
A book that's handy is 'Local Bread" by Daniel Leader.