Microsoft confirms Skype has been optimized to work on older Android devices

The new version of Skype is smaller in size and eats less memory, thus allowing for greater speed and better audio and video quality on budget-friendly Android devices. Moreover, Microsoft promises the lighter version of Skype will offer increased performance even in areas with “challenging network conditions.”
Those who absolutely must have the new version of Skype before it goes live, can sign up for the Skype Insider Program and take advantage of the new experience offered.
source: Skype, Skype Insider Program