Drones aren't really my thing, but I think you're just all-around going about this completely wrong.
The mobotix M15D is really not that impressive as thermal cameras go. It's also kinda big and a little weighty. I would just use a FLIR Tau module or DRS Tamarisk module, you'll get a better image out of a smaller and lighter package.
The lightbride handles HD video, which is going to be on the order of 7-14x the resolution of a couple of thermal camera modules. Again, wrong tool for the job there are analog video transmitters that are cheaper and designed to work directly with the video feed from a simple thermal module.
Making the Mobotix camera work with the lightbridge is going to require some sort of IP->HDMI decoder/transcoder in the middle. That adds more weight and more power budget. You're going to have a flight time of 5 minutes.
Why do you want to use thermal cameras? Are you trying to do something that specifically revolves around thermal video? Do you need *live* thermal video, or can you put a small sd-card recorder on-board?