step:
options: selected: save window state(position,size,bookmarks,...)
selected:autosave desktop

1.open one package body file: mypkgbody.bdy
2.set some bookmarks on mypkgbody.bdy
3.close plsql v15.0.1( do not close mypkgbody.bdy)
4.open files.info, there are below bookmarks:
BookmarkY0=8
BookmarkX0=0
BookmarkTop0=8
BookmarkName0=
BookmarkY1=6
BookmarkX1=0
BookmarkTop1=6
BookmarkName1=

5. open plsql v15.0.1
6. there are not bookmarks on mypkgbody.bdy

ps: plsql v14 is ok

ps:
1.open plsql v15.0.1
2. set some bookmarks on mypkgbody.bdy
3. close mypkgbody.bdy and close plsql v15.0.1
4. open plsql v15.0.1
5. open mypkgbody.bdy
6. bookmarks is exists on mypkgbody.bdy ---> OK

I can indeed reproduce this. The bookmarks are saved when you close the Program Window, and they are not saved when you close PL/SQL Developer. We'll fix it.