You can turn it off by modifying the script file for MIG-15. The file is
C:\Program Files (x86)\Steam\steamapps\common\DCSWorld\Mods\aircraft\MiG-15bis\Cockpit\Scripts\mainpanel_init.lua
To turn off autolean, set it to false:
autoLeanToAimMiG15 = false
Just to throw in as a bonus, you may want to also switch off auto hunker down for F-86 (if you have the module). Here is how to disable head height adjustment that happens after you take off:
C:\Program Files (x86)\Steam\steamapps\common\DCSWorld\Mods\aircraft\F-86\Cockpit\Scripts\mainpanel_init.lua
landSeatAdjustF86 = false
