The latest version of Android is painfully slow - on my Sony Z3 it is nearly impossible to use. The previous version were also annoyingly slow and took up a lot of space.
Is there an alternative version of Skype that is more convenient to use?
Yes there is! In February 2017 Microsoft introduced a new version of their app called Skype Lite, which is a lot faster. According to the official page the new version is:
Lightweight, battery-friendly and runs smoothly on new and old Android mobile devices.
Since sometime in 2018 it became available to all users worldwide, so you can install it directly from the Play Store.
NB: I do not work for Microsoft and have nothing to do with the development of this app.