This is the big one. Quite a few times while Windows 10 Mobile was still in beta, I ran speed tests comparing the OS to Windows Phone 8.1. Windows Phone 8.1 would typically win and I’d conclude that it’s to be expected since Windows 10 Mobile has more features.
My theory has remained the same. Windows Phone 7, Windows Phone 8, Windows Phone 8.1, and Windows 10 Mobile have all added significant features to the OS. All of the earlier versions have always been lacking in one area or another. This is how Windows Phone got its reputation of being “light”. There’s nothing magical about it. It was just lacking key features. As Windows Phone matures, you can expect it to require more resources.
Of course, there were those that clung to the believe that Windows Phone 8.1 was only faster because Windows 10 Mobile was still in preview. Now, we have the RTM build, so here is the definitive speed test between Windows 10 Mobile Insider Preview build 10586 and Windows Phone 8.1.