Quote from Ledhead27:
"I'd say, given the conditions, de-ice prior to the early morning departure is almost a certainty."
Not necessarily: it depends on the dewpoint, which we don't have. Not much moisture in the air at -15C even if relative humidity reaches the nineties. But if on the day the whole airframe has to be de-iced anyway, I think you've taken the point that the whole issue of the wintry conditions becomes less relevant to your decision (to tanker or not). As JammedStab and I have said, Munich2's runway lengths (LDAs) make the landing weight irrelevant. (Other German airfields with only one long runway might be a different story, e.g., if it was closed or partly closed for WIP.)
Perhaps I should have commented previously that the combination of the very cold conditions and the overnight parking of the a/c represent a very different scenario from a quick turn-round when the airfield temperature is around zero. If the first sector was only an hour or so, and particularly if it started from a much milder place (such as London and Hurn often are), the fuel temperature on arrival might still be higher than your -15C. In that case, frost formation on arrival would not happen on top or bottom of the tanks. Overnight, the fuel temperature would fall to ambient, so its presence would be irrelevant to the skin temperature top or bottom. OTOH, if the a/c had flown a long way from a very cold airfield, particularly from one which uses bowsers (rather than underground hydrants) for refuelling, the fuel temp might have been lower than -15C even before departure. On arrival at Munich, if frost forms on the top of any full tank immediately after landing (see my previous post), it is likely still to be present in the morning - even if the rest of the airframe is clear.
Too many variables, I'm afraid... De-icing is an expensive business on a large a/c. But it is possible to mitigate the cost by ordering wings only, or wings and tailplane.
BTW, I now see that I missed another important criterion for whether you can carry enough fuel into Munich to operate the next sector (or maybe two, as Meikleour proposes) without refuelling: the payload-dependent ZFW (zero-fuel weight) on the first sector subtracted from the RLW (regulated max landing weight) for the conditions. And of course the payload for the next sector may shoot up overnight, giving a higher-than-expected ZFW that would increase the fuel requirement. It may be possible to allow for that possibility by loading a bit extra. But you can't cater for every eventuality!