Update CHANGELOG

CHANGELOG

+v3.15.2
+* Implement new monitoring signal
+* Implement new DAQ (down-sampled and internal channels)
+* Extend calibration for all related values
+* Include Reference Compensation Monitor
+* Improve tests and include tests for all new functionalities
+* Include controller input selector PV
+* Include Main/Secondary concept
+* Add LPS Interlock PV
+* Set Near IQ N and Near IQ M at IOC boot and remove PVs 
+* Fix Notch filter to avoid division by 0
+* Fix table mode
+* Upgrade supported firmware version to 0.6.0
+* Improve OPIs to reflect new functionalities
+* Update module to use sis8300llrfdrv version 5.6.1
+* Update module to use sis8300 version 2.10.2
+* Update module to use sis8300drv version 4.9.0
+
+
 v3.14.3
 * Update module to use sis8300 v2.9.3