Yes, Lenovo Z5s support 4G VoLTE in both sim slots. You will surely experience enhanced voice quality and faster internet browsing and download speed. You can also use its native video calling feature for video calls.
You can find complete specifications here: Lenovo Z5s
Yes, the Lenovo Z5S does support 4G in both the SIMs with VoLTE.
The bands it support are-
4G Bands: TD-LTE 2300(band 40)
FD-LTE 1800(band 3)
3G Bands: UMTS 1900 / 2100 / 850 / 900 MHz
2G Bands: GSM 1800 / 1900 / 850 / 900 MHz
Check its full specifications Lenovo Z5S