I've been using a 1st generation Nexus 7 ("Grouper") for many years running Android 4.3. I recently decided to update it with a clean factory image to the latest available version 5.1.1. It became so slow as to be virtually unusable.
Long story short, I solved the problem by installing the latest nightly build of Cyanogenmod 12.1 (which is based on 5.1.1) and it's like having a new tablet. To do this involves unlocking the bootloader (which will wipe your device) installing TWRP custom recovery and rooting. I also changed the file system to F2FS in certain partitions.
I'm not by any means an Android dweeb, but I managed this in an evening and the results are startling.
If anyone would like help with this do let me know.

Thanks for the replies, I'll let it update.

I'm also using a Nexus 7 (2013) running Android 6.0.1 and everything is absolutely fine.

M

The original Nexus 7 had real problems with 6 when it was released. My wife's tablet is still running this, and is horrible. I put mine back to 5 and its performance was acceptable again.

I recently updated to a second gen Nexus 7, and this handles the latest Android just fine.

Andy

I'm using a Nexus 7 (2013) running Android 6.0.1 (Lollipop) and I have experienced no problems. There were problems with Lollipop when it was first released, but version 6.0.1 fixed them.

Mike
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Hello, my old Nexus 7 threw in the towel earler this year, so since I have been using an IPAD mini, which is very nice, but has to go on my knee as it wont fit on my panel.
So today I bought another Nexus7, it is Running Android 5. something and has automaticlly downloaded an updated Android version, should I install it?, I have memories of android 5 messing up my earlier 2012 Nexus and having terrible problems rolling back.

any advice on stable android versions appreciated (the Nexus will be dedicated to Skydemon and some weather apps)

cheers, Russ_H