Not sure if this is a proper comparison, but I have an HP1000 clone weather station with a tipping bucket, and an RG-15 sensor, both connected to my "Home Assistant" home automation system.
I have found very little correlation between the two. The RG-15 is very sensitive in that (for example) today it has not rained but the RG-15 has measured 0.02mm and then a little later another 0.01mm. Yesterday (again no rain) it measured a total of 0.27mm for the day. The HP1000 clone measured nothing.
On the other hand, on days when it has rained, the HP1000 typically measures about 2 to 4 times the rainfall of the RG-15.
To be fair, they are in different locations but both have about the same view of the sky.
I am disappointed in the RG-15 as I was hoping to create a 'solid state' weather station with the RG-15.
(Actually, looking at the RG-15 daily rainfall graph from my HA system for the last 2 weeks, I wonder if it is not being impacted by the sun - just about every afternoon it suddenly measures between 0.17mm and 0.7mm!!! with no rainfall on those days. Hmmmm)
My RG-15 is connected via the UART to a XBee3 running Micropython that is sending the data back to the HA system. I must admit I can't see how that wodl be altering the data being sent by the RG-15.)
Susan