They don't know their Lalvin yeast at all then... Info is readily available online, and they should have the spec sheets on hand...
http://www.lalvinyeast.com/strains.asp#
With the OG of your must, you're looking at ~12% ABV there... IF you don't stabilize it before adding more honey (it involves a few steps, which I've never done, since I make mine strong enough to go to dry closer to the yeast's tolerance) you'll either have a carbonated mead, or potential bombs...
I would be cautious about putting the batch into anything other than beer or champagne bottles.
The only options for getting it to not be dry are stabilizing it and adding more honey until it's closer to where you want it (don't go to where you want it now, since it will get sweeter/mellow as it ages) or adding more honey until it's fermented to the tolerance of the yeast, or to where the yeast stops, then add a bit more slowly...
If the person that told you that the Lalvin strain maxed out at 14% wasn't the owner, I'd tell the owner to educate their people on yeast... OR, tell him/them to at least use the reference material readily available until they KNOW the yeasts parameters. Giving such bad advice is horrible. IF I had a HBS that gave me that advice, and I found out how bad it was, I would stop going there. Unless the owner took care of things.
I'm sure HAD you been told that the yeast would go to ~18%, you probably would have selected another... For one thing D47 goes to ~14%... Keep in mind, the yeast can hit it's actual max a little lower, or higher, than the published amounts. But not by ~4%, maybe 1-2% variance (max)... If you ferment a bit warmer (within it's temperature range) then you could push it higher. Cooler and you could hit a lower level. BUT, I would not suggest doing that (lower that is) unless you plan to either filter the mead, or stabilize it. Especially if you plan to back sweeten it at all.
BTW, if you like the honey, and you like alcohol, there's a 99% chance you'll like the mead. I wouldn't make mead with honey that I didn't like the flavor of.