BE2015 platform; & Symantec backup software differences?

Backup Exec Does file level backup ... Backup exec System recovery take a Block or secotor level backup. The basic difference is  BESR is recovery software...Backup Exec is a application based Backup and Restore software (Exchange, SQL etc, Windows Systems) where as the main function of Backup Exec System Recovery is DISASTER RECOVERY SOFTWARE (SPECIALLY MENT FOR DISASTER RECOVERY)

BESR is designed to to do a Bare Metal restore to any hardware supported by the OS.

Symantec Ghost Solution Suite can create images of operating systems, user files and settings, and installed updates using the sector-based method of imaging. http://www.sytru.co.uk/ghost-solution-suite

Can Backup Exec 2015 run on Windows 8.1?

No. BE 15 requires server-grade 64-bit OS.  See the SCL below

http://www.symantec.com/docs/TECH227896