This is just too funny (to me)!
Just take your parents to your local knife shop (or outdoor store that sells knives) and show them what a really BIG folder looks like.
The Link and Blur (which I both own) to me are definitely on the small size and one reason (among others) that I don't carry them is because I think that they are too small. My preferrred carry size is 3 5/8-4" and the Link/Blur are only 3.25-3.4" long.
At least your parents are "cool" w/you carrying "a knife" to begin with. I could see a lot of parents objecting to a 15 yr old boy carrying one at the outset, especially if it's illegal (which is probably is) to carry it to school w/you.
Anyway, good luck convincing your parents that the Link and Blur aren't THAT big after all.
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BTW, if you are successful in doing this AND want to "upgrade" you choice of an EDC Kershaw blade, I recommend that you try to get the Shallot 1840.
It's been long discontinued but it was/still is my favorite Kershaw based on looks/feel out of the roughly 90+ Kershaws that I own. I like it so, much so that I own 8 variations of it but it has a 3.5" blade which is longer than both the Link & Blur and will cost you a min of $100 in the 2ndary market for one in good shape w/the box but it's worth it IMO.
Just keep it in mind if you can't buy one now. Good luck!