Generally, warrants do not expire. The warrant likely still exists.
The best way to find out is to have a third party (probably a friend, not a family member) call the police departments and check on this issue for you. Whoever calls should not divulge their relationship with you.
There is no Statute of Limitations issue here.
In NC, generally, a warrant is recalled after 120 days and returned to the issuing Clerk of Court (otherwise officers would have to ride around with filing cabinets full of warrants). This doesn't make the case go away, it just means no one is actively looking for you.
You need to appear in Forsyth County (ideally with a local attorney) and try to get it resolved. They are not likely to have the evidence necessary to prosecute you (no officer, or no officer that remembers a 15 year old DWI), so an attorney may be able to get it dismissed.
If you don't resolve it, it will continue to hang over your head, prevent you from getting a license, and as the NC Courts continue to improve the technology associated with their databases you run the risk of being arrested on that old case any time you run into an officer.