Web Viewer 11.5 has a history file that is a record of all the maintenance that was applied. APPLYPTF writes to the history file. The history file from the OMWV server is usually found in the folder: C:\Program Files\CA\UnicenterOutputManagementWebViewer and will be called by the machine name for the server with a .HIS extension.
It can be a little challenging to interpret, but when you scroll to the bottom, you will see the last PTF applied. If it is RO97315 , that is RO97315 R11.5 SP00 LEVEL SET #4 and is cumulative and will indicate that you have all the maintenance applied that is available for Web Viewer 11.5.