By Default, when installing the IGA V15.0, it writes and installs all relevant files to the / root folder, and it creates the opt directory inside it.
IGA V15.0
Doesn't give an option to select the installation path
The IGA V15.0 installs in a default location without any option to select a custom path. To customize the installation path, the Engineering Team has provided a patch.
File Name:igaxpress-1.0.3-7.tar.gz
Please raise a support ticket and request the patch.
Reference Defect# DE649835