When will Spork 15 be activated?
When all masternodes go to DIP3?
There are still too few masternodes on DIP3. This will change with the next release, however, which will include a simple one-click-update to DIP3, see
https://github.com/Krekeler/documentchain/commit/91c66145a1ac43b5442c29bf4f5bf78e3ebeaa76The gap between blocks can sometimes reach 30 minutes, very unevenly.
Will a more advanced difficulty adjustment mechanism be implemented?
The frequent long block time is due to the Yescrypt algorithm. This can certainly be improved, but it is not really a problem.