Sometimes I unlock my 3GS and it takes 15 seconds before anything happens. Once that happens, it takes maybe another 8 seconds to open the music app.
It's pretty slow on 5.0.1. I think this is the end of the line for updates.
Something is wrong with your phone. You need to do a clean restore. When I had the 3GS it ran smooth and fast on 5.0.1, better than 4.anything.