I think your saving grace here is that you didn't have any full body photos up. Because on anyone less then 6 feet tall or so, 15 pounds is absolutely always very obvious to anyone who pays attention to weight. Now not everyone does, so not everyone can really see the difference, but to someone who pays attention to body size, anything over 10 lbs is not going to go unnoticed.
However if this person wants to go on a date with you having only seen chest and head photos, then this person probably isn't too worried about the rest of you.
I know for me, I make a point on my dating profile to mention "all photos are from within the last 18 months and most recent are the ones..." I also make a point of having not only having pictures where I think I look good, but also plenty where I think I look awful - I figure if I think I look bad in 50% of photos, its probably that I actually look like that at least 50% of the time, and I'd rather someone see me for who I am (and reject me in private) then only show my very best looks and then show up in real life significantly less perfect. Plus some of the pictures where I think I look like a dork, I've been told are the ones where I look "cute" or "approachable", etc so I bear in mind other people's preferences are not the same as mine.