Thats just my experience, though. I'd give it a try, on you it may feel and carry comfortably. Everything about the pack was superb, apart from the fact that it wasn't comfortable on me
I'm coming around to the idea that packs are harder, for me, to 'get right' (in terms of the fit, comfort factor and 'feel') than footwear.
Don't give up on a rucksack because it doesn't fit someone else Really!
I don't fit Ospreys at all either, but an awful lot of people seem to. This is why you have to try rucksacks on first. It can be at least as hard to find a good fitting rucksack as clothing, and far harder to tell what'll fit in advance/over the net.
I know i fit the larger rucksacks ... just need to get to my nearest osprey stockists and check out the smaller day packs, i think its going to fit, but would rather try before sheelling out the money ... if you know what a mean
Anything that fits me Which based on a fair bit of recent testing seems to be the classic 32 / a Villain. No doubt some other sacs but I've tried quite a few Semi frameless packs are certainly worth a try if struggling as they are a bit more flexible (the Villain didn't really fit right with its original, stiffer platformat in) . Luckily they're also rather nice, light sacs with lots of pockets etc so I'm happy!
I've got a longish back, thinnish waist and thin shoulders. A lot of adjustable sacks simply lever off the top of my back, I guess due to the shoulders straps not really fitting right. That was certainly my issue with the Kestrel I tried at length last summer. Also I think with the adjustable Deuter's I had - decent fit on the waist belt but never quite fitted right somehow.
I've also found myself simply walking out of quite a few (perfectly good!) waist belts for whatever reason. That is me of course! A lot of tall people don't fit the OMM sacs at all as they only do one back length.
As Mike says I think ~15L is fine for summer day walks. I'm looking for one. Given what fits me its not easy to better the classic 32 right now. The Ace L seems to fit me nicely but is a bit too similar really.
I've got a longish back, thinnish waist and thin shoulders. A lot of adjustable sacks simply lever off the top of my back, I guess due to the shoulders straps not really fitting right. That was certainly my issue with the Kestrel I tried at length last summer.
I could have written that I'm also using a Classic 32, recently purchased, at the moment
I'm looking to add an Advent Pro (Gregory) to this, for slightly heavier loads, due to the 'semi frameless' nature of it's moulded back panel, the 'mark one' version that I borrowed was superb. I use a Gregory Iso for light, summer loads.
Which based on a fair bit of recent testing seems to be the classic 32 / a Villain. No doubt some other sacs but I've tried quite a few 
