Remove -XX:MaxPermSize=512m from the shipped .jvmopts files and the SysV init scripts; Java 21 does not recognize it, so the 3.15.0 backend services failed to start
Requires Java 21 (3.14 and earlier ran on Java 8). The services start with /usr/bin/java, so if java -version does not report 21, select Java 21 with sudo alternatives --config java
Upgrades replace only /etc/ticrypt/*.jvmopts files you have not edited. Remove the option from edited ones with sudo sed -i '/MaxPermSize/d' /etc/ticrypt/*.jvmopts, then restart the backend services