Yeap, There's no way factory 115cc 2 stroke air cooled road bike can reach 160++kmh, Indonesian RXS (115c) max 120Kmh, RX135 130-140, RZR/RXZ 150-155KMh. except for sport types like: Yamaha TZ125, TZM, Honda NSR150SP, Kawasaki Ninja 150, etc. Those bike can easily reach 170-180KMh.
Have you tested your bike with TZM, Ninja 150 or NSR150...? Believe me, they are much much faster than RXZ ahha.