knime not using Max memory java, why?

Hi,

I set up knime.ini in order to increase the java memory knime should use. I set:

-Xmx16G-XX
MaxPermSize=2048m

but when executing heavy streams, that perform joins and transformation over millions records tables, and setting some nodes to 'memory execution', PC reaches a maximum 7.5GB use of memory and then has to use HDD.

knime 3.1.1 64b

System: i7 recent generation, 24GB RAM, windows 10 64b

Can anyone help?? I need knime to use all the memory allocated, as it would dramatically improve performance (I expect so), which is quite poor now.

Thanks a lot in advance!