Agree, top him out at 60 depending on how many back-2-backs there are. But that's it, 55 is an ideal number.
You can look at the finish of almost every Tuukka season, and fatigue played a factor. Simply put, everyone's body chemistry is different and perhaps fatigue affects him more than others. Like you said he's tall but slight.
Even the great Braeden Holtby looked fairly pedestrian in the last two playoffs after being over-worked in the regular season.
What's troubling is this is the 3rd consecutive year they have encountered this issue, and management seems to either not realize the problem, or be incapable of fixing it.