All the UAVs and drones we've seen to date in 15mm have been very human in origin. There's nothing that Chad Feldheimer could really call serious 'alien shit'.
Browsing Forbiden Planet's store in Aberdeen a couple of month's back I came across these dim sum with tentacles greeblies in a Dr Weller (?) Stargate SG1 Action Figure blister. Definitely 'alien shit' and better still reduced to just £1.99.
I was instantly taken. I'm not into the Action Figure thing but always check them outto see if the accessories would be picking up for 15mm, either on Ebay or if the figure was at a suitably reduced price. In this case, just £1.99 - so I bought three.
I'm going to mount them on individual flight bases as 'extreme' alien remotely or articifial intelligence piloted UAVs/drones. They could also be drop pods, some form of alien jet-bike or just a missile. With some pinning, you could stand them vertically as walking/floating alien mechanical or biological multipods.