2.10 tire on 15mm rim - how dangerous?

So, last night it occurred to me to mount my Primo Comets (20x2.10/54-406) on my Speed D8 in place of the OEM Schwalbe Marathon Supremes (20x1.60/42-406). Problem is, the Speed's OE rims are 15mm (vs. the Vybe's 19mm rims.) I've had a hard enough time taking the Marathons off, managing to punch a...