SQL memory usage with freetext indexing
As Shanky implied in the comments, your Max Server Memory value is probably not changed from the default. SQL is designed to use everything at its disposal.

I've written a script, based off work from Jonathan Kehayias of SQLskills, that will let you know the value you should use.

Jon advises reserving the following amount of RAM for the operating system:


1 GB of RAM for the OS
plus 1 GB for each 4 GB of RAM installed from 4 – 16 GB
plus 1 GB for every 8 GB RAM installed above 16 GB RAM


Anything left over from that, can be allocated to SQL Server, assuming it's a dedicated instance.

If your VM only has 6 GB available, the recommended value is 3 GB. To change it, you would write something like this (or change it in the Management Studio UI):

EXEC sp_configure 'show advanced', 1;
EXEC sp_configure 'max server memory (MB)', 3072;
RECONFIGURE WITH OVERRIDE;
GO