Looking at the error: package sun.util.calendar is not visible, this is likely due to the difference in java versions between IS 10.5 and IS 10.15 , since 10.15 uses Java 11 and some packages were not made available.
The sun.util packages are supposed to be internal, I would suggest you check for any alternatives to sun.util.calendar.BaseCalendar.Date and see if it works for you.
Reference : Stackoverflow- Upgrading to Java 11 from Java 8 - package sun.util does not exist - Stack Overflow
-NP