which Junos for my EX4200

Hi all,

my company have plenty of EX4200 : a lot of them have an old version of JunOS ( 12.3R6.6 ).

I would like to update them but JTAC Recommended release for this product is 12.3R12. ( and EOS is the 31-Jul-2017 )

Does there is the possibility to update to 15.1R4 ? i don't understand difference between this two versions (except the support of SDN )

thanks for your help

cordially