Hello, this works for me on Sphere 99 and 306m client.
_arm command equips items by double clicking on them.
You could try to write a script:
UO.Equip subrutine pickups the item first and then equips it to the requested layer. Maybe it could solve your issue.
I'm not sure if 2015 supports 7.0.30 clients. Anyway I don't see any protocol changes that could affect _arm command. So maybe the problem is server related. Are you able to downgrade client version?
There is a discord channel related to infusion scripting: https://discord.gg/6ZmqWbA