Since beta 2 a constantly have such issue.
I'm using several workspaces with 20 - 60 tabs in each of it.
I'm starting each instance of PL/SQL Developer using shortcuts with Target string like
"C:\Program Files\PLSQL Developer 15 Beta\plsqldev.exe" workset="wrkspc1" "env:NLS_TIMESTAMP_FORMAT=YYYY-MM-DD HH24:MI:SS.FF" "env:NLS_TIMESTAMP_TZ_FORMAT=YYYY-MM-DD HH24:MI:SS.FF"

After doublclicking on a shortcut the splash screen of a PL/SQL Developer appears, and most of times main window drawing behind the splash screen. But after few second application crashes and close without any message. Also i don't see correspond logs in plsqldev.elf. Maybe need some additional option for debug logging.

But i found a cargo cult action to prevent a crash: when main window drawing behind the splash and we see nothing in windows tab, code section etc. - if i make several clicks on then drawing main window, right on the empty space where code will be showing, the PL/SQL Developer continue work and some time later all tabs restoring become completed.

There is feel like when i'm clicking on the main window, some background thread slowing down, get all date/objects that it need, and didn't broke all application start.

To obtain some more diagnostic information, can you modify the PL/SQL Developer shortcut and add the DebugSQL parameter? For example:

"C:\Program Files\PLSQL Developer 15\ Betaplsqldev.exe" DebugSQL

Reproduce the problem and send me the debug.txt file that is generated in the %APPDATA%\PLSQL Developer 15 directory (e.g. C:\Users\<User>\AppData\Roaming\PLSQL Developer 15).

I did make 3 tests and find that debug file constains different string at the end. So i put all 3 files in attachment archive.
Also i replaced all private data like user name and connection name. Because of the second file was the smallest, i just did replace such data in it, but in 1 and 3 files i simple remove the block with words "UpdateConnections.Clear". It's the same for all files.

Thanks! We'll investigate.