There are many, many, many reasons for the difference in performance. Without a lot more information, there is no way to guess what is affecting your query.
Do the actual query plans match?
Assuming your proc takes parameters, did you try WITH RECOMPLILE on the proc?
Did you install on the same server?
If not, are the VM servers configured the same on the same hardware/disk drives?
How did you get the database into SQL 2014?
Assuming you did a restore, did you rebuild the indexes and stats on SQL 2014 after the restore?
Enterprise edition uses all CPU/RAM, Standard edition is limited. Do you have >4 CPUs? Did you configure more than 1 core per socket in your VM?