I don't think it's going to take 10-15 years. It just depends on the manufacturer of the LED. Philips has an excellent reputation and have been shown in torture tests to hold up very well. And I recently got a case of the Philips three-lobed LEDs, honest-to-God 60-watt equivalent, standard bulb shape and profile, to try them out. Much better light than fluorescents, come on almost instantly and at full brightness (eat your heart out, CFLs), dimmable, and use only 12 watts (the new and more expensive model uses 10 and puts out 70 watts of light). Cost was only $14 each--that's already paying for themselves in two years, probably less in the applications I have in mind. Yeah, I could use CFLs, and probably save money overall, but I like the quality of the light from the LEDs, the dimming and the instant full brightness. That's not to say they don't have a ways to go. They still don't have a hundred-watt equivalent LED that fits in a standard profile.
I noticed Lowes is selling 1400-lumen par38 bulbs for less than $40 each, I might give them a try. What a novel idea--energy efficient outside lights that actually come on instantly. Can't imagine why you'd want that, eh?
But as far as shop lights go, LED doesn't have enough advantages over T8s to make them worth the cost.