Finally sucessful update BV5000 into Marshmallow.
With this ROM file:https://mega.nz/#!X98HRbJZ!Tyv0GKb8L_SG
I suppose it's latest one.
I used this flash tutorial:viewtopic.php?f=96&t=1027
This driver:http://spflashtool.com/download/Driver_ ... 236.00.zip
And this SPTool:http://spflashtool.com/download/SP_Flas ... 00.000.zip
After succesfull install driver as Admin. I run SPTool. Choose "MTK_AllInOne_DA.bin" from SPTool folder. Choose "MT6735M_Android_scatter.txt" from unpacked ROM folder. Click "Dosnload" in SPTool. Then plug in switched off phone into USB port to PC. Download ROM starts immediately and automatically. After 2-3 minutes appears green circle with "OK" description. Now we can switch off phone from USB port and power it on. After 2-3 minutes of phone start we can use the phone.
I see no errors so far with using BV5000 on this ROM. Everything works stable and faster than on Android 5.1.