Hi Muddassar,
SAP has provided brilliant migration tools using which you can migrate from any lower version to higher version. I did it for 11.5 to 14.0. 11.5 was the most varied version as compared to 12.0, and I was able to do it easily with knowledge of some prerequisites and pre migration checks.
So you can directly migrate from 12.0 to 15.0. Make sure, you have a 7.31+ NW system that hosts 15.0.
Thanks and Regards,
Swaroop
