I use to raise and lower the mast on my Hobie 16 all the time, single handed. I have watched the guys with Hobie 18 and Nacra 5.5, raise and lower their masts single handed too. They get pretty creative with rigs for raising and lowering. Necessity is the mother of invention.
Your Vanguard 15 isn't that much different than a Laser or JY. The sailing club has tons of those and 15 y/o's put those up.
I don't want you to think that I am saying something like "geeze even a 15 y/o can do it" I can tell you I have dropped my Hobie mast several times (never damaging a car, or passerby). I have seen others drop their masts and really break things (mast plates or masts themselves).
Stepping a mast is a REALLY awkward task. You are trying to focus on several things, most of which you can't reach as you are putting a mast up.
What exactly is the problem you are having? Maybe if you could put together a drawing or two, we could help you figure out where you are having issues.
To part of your original question, I wouldn't change to a different mast or sail plan. The expense of it doesn't make sense. Besides the mast, sails (main and jib will need to be smaller), and any of the standing rigging would have to be replaced.