Viewing the history on the Timeline card on my site can take several minutes to load. I'm assuming this is because there are 155 older versions of the card? But it makes actually using the fact that there's a history and that it autosaves things really difficult. Viewing a history takes a long time normally but this reaches unusable.
It's not the number of versions, it's the length of the card. Wagn's algorithm for "diffing" (finding the differences between) two versions is not fast enough, and it gets worse and worse the longer the card is.
We need to improve this, but as a workaround you might consider breaking it up into a few separate cards (eg by month).
You can also use "hide changes" to scroll through revisions more quickly (after the first one).
The whole revision handling system is being upgraded by the way. Some big improvements coming...