NC 155 appeared about 1995 as a renumbering of US 321 in the Boger City area.
By 1998, NC 155 replaced old US 321 south to NC 274-279 Dallas (was secondary for a time since US 321 freeway from Dallas to High Shoals was opened in the late 1980s) and was added to US 321 from Boger City north to US 64-70 Conover. Note that the freeway stub northwest from Boger City to Starwood Rd was initially opened as SRs 1844 and 2913.
In June 1999 (NCDOT), NC 155 was renumbered as US 321 Business.
Steffora reported that public opposition to losing the US route designation for communities along NC 155 drove the change in numbering. He also reported that signage for NC 155 was spotty and in some cases non-existant, especially in Newton/Conover, which was still officially US 321 until June 1999.

US 321 from Dallas to Conover 1993 Official

NC 155 from Dallas to Conover 1999 Official