After paid off would bring in about 10-15K a month in rent and equity of 2 mil today's numbers (hopefully double in those 15 years).  4 rentals in texas 2 out of state.

According to the US census data Los Angeles, CA county population declined 3.5% in the last few years as you can see here:(Data from April 2020 - July 2023).But Real Estate prices went up in that period 25% according to Zillow (From $665,868 to $834,772).Rents went up 18% (From $2,380 to $2,827).How that can be?

Since your keen to invest where you live, and want to do STR's, keep an eye out on increasing restrictions. 

Buildium our property management software does not provide credit bureau reporting as service, despite request over many month from many of it's users.  It is suggested that  "Small" landlords use a collection agency,...

The house had gone up in value a lot and he thought he deserved the increased equity.

It can be move-in ready and could use some TLC to increase the value of the home.

Also keep in mind that adding sqft will likely increase your taxes and local regulations might limit the use of the ADU. 

I currently rent out in San Diego.Mohit

It can be a negative factor if there's increased traffic/noise or if it blocks off a view. 

It's great for me because I can get a unit-by-unit understanding of collected rent.