No manufacturer ever released an official over-the-air (OTA) update from 4.4.2 to 7.0. That’s a 3-year technology gap. Hardware drivers for cameras, Wi-Fi, and Bluetooth on 2013-era chipsets were never designed for Nougat.
: Android 7.0 is significantly heavier than 4.4.2. If your device has less than 1GB of RAM, it may lag significantly even if the installation is "verified." android 442 update to 70 verified
This is the only "verified" way to get 7.0 on an old device. Developers create custom software versions based on the Android Open Source Project (AOSP). No manufacturer ever released an official over-the-air (OTA)