The bad news is that getting good windward speed and height can be difficult. The good news is that it's mostly dependent on crew

Having good sails is neccesary, if they are really old, they are probably shot.
Unless you find a Venture 15 "guru" who can tell you what the optimum rig settings are, you can gain much by experimenting with mast rake, crew position and sail trim (most beginners dont sheet the sails hard enough). Time spent on the water, sailing your boat to windward, is the best way to learn how to make it fly.

If you have a boardless cat (it sounds like you do), it's generally better to foot off and keep your speed instead of pinching up.