The autosave settings get reset to default every time I restart.

Since Adobe are still investigating this really difficult question, here’s an actual solution by somebody who’s fed up of crashes and losing work progress:

1. Close Substance Painter if you have it open.

2. Open this file with Notepad++
   
   "C:\Program Files\Adobe\Adobe Substance 3D Painter\resources\application_plugins\autosave\ConfigurePanel.qml" 

3. and change this value to whatever you want
   “readonly property int intervalDefault”
    

4. Keep in mind that  if you set it to lower than 10 minutes you’ll have to also change the minimum cap here as well 
   qsTr("Autosave interval in minutes:")

5. Save “ConfigurePanel.qml” 

Done. You’re welcome.