If the driver got installed by Windows Update on 64-bit Windows. Then you will never get driver to add it in additional drivers of x86 on 64-bit machine for sharing! because upon investigation i understand HP didn't write for it or don't have it for P2015 on PCL6!
Workaround one: You need to delete/uninstall the driver from Windows Update then download and extract HP LaserJet Universal Driver PCL6 for both x64 and x86. (Make sure they are on same version by Driver Deployment Utility.) Install x64 first on 64-bit windows 7 pc on which printer is connected then go to sharing click additional drivers install x86 driver on it. Now you can share this printer with x86 clients! just give \\computername\HP LaserJet Universal Driver PCL6 then connect. That's all.
Workaround two:
You can also go to client computer direct (x86 which needs to connected with 64-bit) just install Universal driver for PCL6 on the network selection choose the last option put \\computername\HP LaserJet P2015 PCL6 then click connect but it will show it is not connected! never mind. Click okay. It will get installed. Try print a test page and see.
(Here you dont need to uninstall windows update driver on destination printer ie., x64-bit to whom the printer was connected)