Perhaps too sweet?

Hello I think I may have under fermented my Belgian wit. It fermented for around 14-16 days at temps ranging from 68-70 f. I didn’t notice any more bubbles from the airlock and I know this isn’t the best way to know if it is done. I didn’t have a hydrometer at the time. When I transferred it to the secondary at day 15 I took a sample and it seemed a bit sweet. If fermentation didn’t finish in the primary would it finish if I just leave it in the secondary without adding additional yeast? I added the White Labs WLP400 which I have read that it may take longer for this strain to completely ferment.

Recipe
Preboil
6 gallons water

Boil
6.6 lbs. 40% wheat/ 60% barley liquid malt extract or:
3.3 lbs. light/pilsner malt extract and 3.3 lbs 100% wheat malt extract (75 minutes)

3/4 oz. Tettnanger (60 minutes)

3/4 oz. Saaz (60 minutes)

1/4 oz. Saaz (flameout)

1/4 oz crushed coriander (flameout)

1/4 oz bitter orange peel (flameout)

1 pinch "secret spice" (flameout)
"secret spice" (anise, cinnamon, vanilla, pepper, or ginger) your choice

Yeast

WhiteLabs WLP400 or WLP410.....or Wyeast 3944 or 3463....ferment at 70 degrees

If there is additional fermentable sugars in the beer it should continue to ferment out in the secondary. Why not pick up a hydrometer now? You should be able to get one at your LHBS for $10ish, and probably cheaper online.
Once you peg a gravity you can at least see if it is still going down.