(here we go again) There's 2 schools of thought. The first does as the OP did, treat them with stuff to make them "pliable".

The second school never soaks them with stuff because pliable = early demise. I subscribe to this. Hard, cracked and old is just fine, just put the occasional swipe of proofhide on top and go. This works for me and I continue ride some very old saddles with great success.

I know it's just an anecdote and some saddles do fail. B-15's are definitely lighter duty than other models.