Efficiently or not, there are things the Nexus can do which the 1520 can't because of the newer specifications. For one thing it supports voice commands even when the phone is off.
It has a 2K display coupled with a Snapdragon 805 processor which allows for faster shot processing and tons of other improvements, and despite graphics already being better on Android the Adreno 420 will also provide a massive boost in graphics quality and speed.
And Android doesn't experience "resuming" and usually gets apps to open up and multitask faster than Windows Phone but still the Nexus 6 will be able to multitask even better because of 3GB RAM.
And lastly your notion about every Android update adds bloat, that is false. Every Android update released in the past few years focuses entirely on making performance better, and this year with 5.0 they have absolutely killed it. It's so smooth and silky, with very few things that they need to iron out, 4.4 was also a major step up in performance from 4.3 and previous versions of Android have done the same.
Also about the bloatware, Android 5.0 actually makes bloatware less of an issue:
http://bgr.com/2014/10/29/android-5-0-lollipop-feature/
Also go ask anyone still rocking a Nexus 4 how their phone is running two years later on Android 5.0 and I'm sure they'll tell you how much faster it has gotten compared to the original 4.2
Please for gods sakes educate yourself before spewing out what you consider "facts".