You are sure that you will not burn your place?
Because it seems like that fan is moving some air out of the usv. If you drastically reduce the cooling, you could run into serious thermal problems. Worst case could be the overheating usv is causing a fire. So, fan swapping yes but keep up abreaonable amount of cooling functionality.
Online Xanto upses have temperature alarm fan and shutdown.
Anyway my idea is to put not a slow fan but a "fast" silent fan (with CFM comparable to original one) and use temperature sensor to lower RPM a bit.