Recent versions of JDK8 javac appear to compile slower than javac from JDK7, even when using -source 7 -target 7 and running on JDK7.

For example, we have measured time needed to compile JDK8 langtools sources using command like this:
${JDK7_HOME}/bin/java -Xbootclasspath:${LAMBDA_HOME}/lib/classes.jar:${JDK7_HOME}/jre/lib/rt.jar -cp ${LAMBDA_HOME}/lib/classes.jar com.sun.tools.javac.Main -source 1.7 -target 1.7 -d build -classpath build -sourcepath src -bootclasspath ${JDK7_HOME}/jre/lib/rt.jar @files

The average times from 10 measurements were:
JDK 7 javac: 17.4s
JDK 8 javac: 22.7s
lambda: 23.0s

Versions used:
JDK7:
$javac -version
javac 1.7.0_15

JDK8 - langtools tip: d3648557391b
Lambda - langtools tip: f55c889a51a5