We are currently converting our iLog rule engine solution to a Drools based system with good success. The project is a Maven project using Spring Boot 1.5.2 and Java 1.8. We have converted 1800+ rules (including 83 decision tables) from their iLog format to Drools format. We were using version 6.2.0. The newKieSession method took approx 2 minutes on the first run to compile our rules and provide the kieSession: -

KieContainer kieContainer = KieServices.Factory.get().newKieClasspathContainer();
KieSession kSession = kieContainer.newKieSession("ric-rules");

I decided to upgrade to version 6.5.0 by updating our pom.xml.

When I ran the code again, the above newKieSession method took 20 minutes to complete. It also seems like our rule processing stalled or hung with no Exceptions being reported.

I have the following dependencies in our pom.xml

<drools.version>6.5.0.Final</drools.version>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>

<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-jdbc</artifactId>
</dependency>

<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-mail</artifactId>
</dependency>

<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
</dependency>

<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>

<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-jms</artifactId>
</dependency>

<dependency>
<groupId>org.kie</groupId>
<artifactId>kie-api</artifactId>
<version>${drools.version}</version>
</dependency>
<dependency>
<groupId>org.drools</groupId>
<artifactId>drools-core</artifactId>
<version>${drools.version}</version>
</dependency>
<dependency>
<groupId>org.drools</groupId>
<artifactId>drools-compiler</artifactId>
<version>${drools.version}</version>
</dependency>
<dependency>
<groupId>org.drools</groupId>
<artifactId>drools-decisiontables</artifactId>
<version>${drools.version}</version>
</dependency>
<dependency>
<groupId>org.drools</groupId>
<artifactId>drools-templates</artifactId>
<version>${drools.version}</version>
</dependency>
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-lang3</artifactId>
<version>3.6</version>
</dependency>

I also found someone else on Stackoverflow with the same/similar issue
https://stackoverflow.com/questions/44406051/drools-6-5-0-drl-compile-time-increased-10-times/44713857#44713857