May be it's not the best time to run 5.1 on mako, at least for me.
Using Nexus Root Toolkit, I have installed apks of Google Play Services, Play Store, Gmail, Google Now Launcher and Google Search but now every time I click on Google Settings or Play Store (even in System Settings --> Accounts--> Add Account--> Google) a pop up persistently appears and says "Unfortunately, Google Play Services has stopped" .
Looks like old apks cannot make friends with new OS version.
Try updating your google play services with Aptoide. The newest version from there worked very well for me.