Seems there is a minor update rolling out for Sprint Moto E 2nd Gen (2015), one that must be patching the Stagefright bug on the device.
The software version that accompanies the update is LPI23.29-18-S.2, the earlier one being just a numeric less at LPI23.29-18-S.1 — the Android 5.1 Lollipop update for the device.
The update hit the release phase today only, September 23, 2015.
Sprint is yet to provide us a changelog of the update but given the minimal software version change, you cannot expect a lot form the update.
Do check under About device menu in Settings for system updates. You must be receiving a notification for the same starting today, and within this week or next one.