You would have to look at the implementation directly. The user documentation isn't great for documenting performance considerations, sadly.

Essentially it comes down to this: a snapshot LV contains copies of old blocks which have been modified in the source LV. Whenever a block is updated in the source LV, LVM will need to check if that block been previously copied into all corresponding snapshot LVs. For each source LV where this is not the case, it will need to copy the block to the snapshot LV.

This means that there is O(n) complexity in the checking and copying. And in the case of "thin" LVs, it will also need to allocate the block to copy to, potentially for every snapshot LV in existence, making the process even slower. The effect is write amplification effectively proportional to the total number of snapshots.

ZFS snapshots, in comparison, cost essentially the same no matter how many you create, because the old blocks are put onto a "deadlist" of the most recent snapshot, and it doesn't need repeating for every other snapshot in existence. Older snapshots can reference them when needed, and if a snapshot is deleted, any blocks still referenced are moved to the next oldest snapshot. Blocks are never copied and only have a single direct owner. This makes the operations cheap.

FreeNAS has good documentation on which hardware to pick and how to set up ZFS.