[fitkoh]

I have a gentle Question here. 
Is the license is compulsory even i go for an older version of JAVA? 
Is it any free service for Linux based servers?
I got download this "jdk-15.0.2_linux-x64_bin.deb" and move to /tmp folder but unable to install it.

I don't know of any specific licensing terms but I'm sure you can find them on oracle's website.
I believe you already have the open version (openjdk & openjre) of JAVA which does not require a license.  You can verify this by your output of  $java -version 

Code: (Select All)

root@kvm-xxxxxxxxxxxxxx:~# java -version
openjdk version "1.8.0_275"
OpenJDK Runtime Environment (build 1.8.0_275-8u275-b01-1~deb9u1-b01)
OpenJDK 64-Bit Server VM (build 25.275-b01, mixed mode)

What command are you using to install the .deb, and what is the output?