I managed to update to JSS15Q. I was running on stock rooted firmware and received the OTA notification. So here's what I did: full unroot via SuperSU, update to JSS15Q and it was all good. TWRP recovery was gone so you need to flash it back. Apply supersu.zip file. And you're now rooted again.
Can I just wait for update thru ota as I just brought N7 last week? Or it is a dreadfully long process for them to roll out on our device?
Err... you're not required to unroot to install the OTA update.
And you should be able to get prompted for OTA if you did not modify your rooted stock rom whatsoever.
In any case, check this post, it has everything you need to get you to JSS15Q whether rooted or not, OTA or full factory image.
JSS15Q replaces JSS15J - Multi-touch, GPS, corrupt eMMC addressed, other fixes? PRNG? - xda-developers
Here's in a nutshell common problems (that I faced) when doing OTA from zip:
1. if you're rooted on SuperSU, you have to download SuperSU and a SuperSU-ota.zip link easily found in the thread post (marked as "see this post"). You only need to reinstall supersu and the ota zip after updating. No need to unroot or re-root the device.
2. If your computer cannot detect your device in adb sideload mode, install the adb driver from
this thread post.
3. for OTA to work, your ROM must be pure stock. If you did any (major/minor) modification to the stock rom, you should flash factory image first. This normally can be done without the need to do a data wipe.
*One of common (forgettable) minor mod people do is Advance Power Menu mod. If this is the only modification you made and you don't want to go through the trouble of reflashing factory image you can just run
this from recovery to restore stock rom before performing OTA.
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Hope that post helped someone here having trouble updating to JSS15Q.

It is a life saver update for me. Completely solved my multi touch issue...
I have absolutely no complaints with the Nexus 7!
Perfect device at a perfect price point.
