1. No, you have to tell it to run the upgrade. Automatic upgrades would be disastrous!
2. No, it can not upgrade from 1.5 to 2.5. You have to use something like jUpgrade or SP Upgrade to perform the partial migration.
Regarding "PHP file changes and security scan" I can't explain it very well in simple English. It reads all your PHP files. It calculates MD5 sums. Next time, it does the same. It compares the MD5 sums. If they are different, the file has changed. If the file has changed you a. upgraded an extension or b. got hacked. Therefore, it lets you know which files have changed. This allows you to figure out if you've been hacked.
I would suggest finding someone who can read better English and translate the documentation page for you. Without reading the documentation page there is no way to make the PHP File Changes and Security Scan feature work properly.
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!