How to run spock unit test in the grails project faster?

We have a project on groovy/grails. For unit testing we use Spock framework. Everytime when I run even one unit test it requires reloading Grails.

|Loading Grails 2.3.5
|Configuring classpath
.
|Environment set to test
..........
|Compiling 1 source files
.....
|Compiling 2 source files
....................................................................................
|Compiling 1 source files
.
|Running 1 unit test...

It takes about 15 seconds.

Can I speed up this process?

p.s. I run tests under Intellij IDEA