I've done it on other trucks (but never after 15 years) by using a hairdrier or the hot sun to soften the adhesive and just start pulling it off. Then use some adhesive remover to get the rest the the glue off. Warning: you know the paint anound the graphics has probably faded a lot in 15 years of sun exposure so there will be a big color difference between the two areas. I did it on a silver truck that was just 2-3 years old and I could tell where the graphics were.

93 4X4 ext-cab, auto, SR5, 3.4 V6, supercharged, 2.1" pulley, URD fuel mods, Aquamist WI, IPT valve body mod, dual cases, 4" superlift, Alcan springs, 33 BFG MT, ARB locked front & rear, 5.29 US Gears, RB 1" BL, 1.5" BJ spacers, TJM T-17, Warn m8000.