I don't know if I am the one and only but for me the Vikings are like an repeating event and allways the same-
It's boring and not profitable enough to have this "stress" especially when a regular event is in the town.
You are not the only one. I talked to plenty of my guild members on my main world and all told me the same: They play just for Yggdrasil and the Emissaries. And after that for the additional 50 FP. But they planning to finish just one settlement per month, if possible. The reward for finishing in time is just too small and too hard to achieve, if you have a real life with work and everything.
And yes, I know, there people here, who don't agree. But please, don't reply to this post just to tell me, that you have also a real life and make it in time. Because there is a small difference between you and me: I don't waste time by producing 5-min or 1-h productions of copper for hours. I don't have the time for that, not even in the evening. And even if I had, I have better things to do.
To make this more attractive, it should be possible to make it in time even if you log in just one or two times a day. It don't have to be the "gold" reward but at least the "silver" reward. And the gaps between the rewards should be smaller, because if you manage to gain just the "bronze" reward you have to play 75 (!!!!!!!!!!!!!!!!!!!) times to gain ONE (!!!!!) GR on Lvl5. With "silver" we still have to play 25 times and with "gold" 9 times. Don't you think, that's too much for one GR? I mean, with "gold" it's fine. That means, we are able to get more than one GR with the 15 playthroughs you're intending to, but as soon as there more cultures added, the most people won't play the vikings again. And they will have a GR on Lvl1 in the inventory and never place it, because it's worse than SoK, because of the lag of population and the smaller amount of gold of a GR. I do also think that the quests should differ a bit each time.