Reduce CMake Requirements to 3.15
The current CMake requirement is 3.17, corresponding to version present on CentOS7. This reduces the requirement to 3.15, which is the default on other OS's (ie: petalinux) and still supports all our functionality.
I don't see anything in the ChangeLog that affects us: 3.16 3.17
The use of cmake_minimum_required forces the behaviour of 3.15 even if the CMake version is newer.
Edited by Karol Krizka