Check out the below URL to fix the issue
http://thenextdigit.com/15284/nexus-7-2012-lag-issues-android-5-0-lollipop-update/
Last week my Nexus 7 tablet was upgraded from 4.xx to 5.xx. Every since then my boot time slowed from two minutes to four minutes. I tried removing everything from startup, but that only shaved about five seconds off the boot. It acts like it doesn't have enough RAM. Any thoughts or suggestions?

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