I hung onto mine until I was 3...my mom finally told me the easter bunny would only leave a basket if I hid my 'binkie' so I did...and in the morning the basket was in its place
I would try going down to 1 (& maybe hide a spare) so it's not easy to grab and find them all over the house if you have several and make a point to have him look for it if he wants it.
If you aren't already, I would also try to limit the time he uses it to the times you think he needs it most (nap time, bed time, etc.)
If he's playing and wanting it, try doing something like blowing bubbles and tell him to blow (I know at that age they can't do that yet) or ABCs/word/talking games but. If his mouth is distracted he might forget about it.
Mine were all thumbsuckers which was hard because I couldn't take that away! I finally had to bribe them with cash! Yes, they were that old
