The best guitar player of the past fifteen years is probably Tom Morello simply because of his ability to take the music that he heard and merge that with his own unique style and take the music further. Listen to that first Rage album and realize that those sounds were created entirely by a four piece band with out a DJ. A lot of the bands that are popular today are simply using a DJ to recreate the sounds that Tom creates on his guitar.
My honorable mentions would have to be Stanley Jordan, Eric Johnson and SRV. Stanley Jordan has taken a very specialized method of playing a guitar and made it his own. See him live if you get a chance. It is amazing. If you think Van Halen when you think of two-hand tapping, buy "Magic Touch" and think again. Unfortunately, his best work (Magic Touch) was done prior to 1988, so he doesn't fit the past 15 years criteria.
Eric Johnson is also amazing, but he hasn't been as revolutionary as Morello or Jordan. It hurts me to not put him first because "Cliffs of Dover" was the reason I picked up the guitar and "East Wes" is the reason I started listening to Wes Montgomery.
SRV is the man, but I feel like a lot of his best work was pre-1988. That said, his sober sessions are gutwrenching. "Life by the Drop" and "Little Wing" bring tears to my eyes every time.
IN general, if you want to hear someone who is still going strong, check out John Scofield. Listen to "Bump" or "A Go Go" and you'll find a man who can squeeze some crazy sounds out of his guitar. He's been going for a long time and he's still churning out some hits.
I give an incredible amount of respect to Wes, Django and Joe Pass, but their contributions over the past 15 years are somewhat minimal. Hendrix, Clapton, Beck, Van Halen, same story....
As for who do I listen to before a race? Slash & Izzy every time...