I would suggest that size is not the issue here, (relative) quality is. As many have mentioned, delivery on a data DVD is doubtful even if it’s a DL. No one really wants a downres’ed SD DVD-formatted project, even if that’s what they’re saying.
Ask, then confirm, broadcast spec, then ask and confirm again. If they never get back to you with a real size and codec spec, I’d deliver a 1080p quicktime at AVID DNxHD 145, stereo 48K linear PCM, big endian. And, I’d ship it (or whatever they ask for, if they do give you spec) on a 64GB (or 32G, or 16G if it fits) USB3 stick, for maximum copy-ability (not every facility has a BD drive, but all have computers with USB3 or 2).
IMHO
Ferd