Disclaimer: My experience comes from building RC models and various other projects over the last 3 decades. I haven't built skis (but that's why I'm on this forum now... I need a project for this winter since I won't be doing any real skiing :-)).
I'm going thru a similar design consideration, because I have a lot of lighter fabric leftover from previous projects.
General thoughts on multiple-light vs. single-heavy layups:
1. Multiple layers allows you to play with the bias a bit, which can be handy. e.g.you do one layer at 0 degrees, and two at 45 degrees.
2. More layers means more work. This can matter if your epoxy/resin has a short pot life and you want to get everything done in one shot.
3. It depends on the specs for each fabric, but I wouldn't be surprised if 3 layers of 6 ounce fabric is as strong as one layer of 22 ounce. Look at
http://www.cstsales.com/fiberglass_data.html for instance.
4. Lighter weight fabrics typically have smoother finishes, if that matters.
5. I'm used to doing applications where weight matters and people do extremely dry layups. Making light/dry layups is harder when doing multiple layers, but for skis nobody seems to talk about minimizing the weight of the resin. Folks seem to just slather it on and let the press squeeze out any excess.
Tl;DR: If I had 6 ounce fabric laying around, I would build something with three layers of it (biasing one or two layers at 45 probably) instead of 22 ounce, and see what happens.