Not sure I agree with your assessment there. Small scale attacks between Kurdish groups and Turkish nationalists, occasionally involving the police and military, have gone on even during the ceasefire periods. I see the resuming of hostilities as having been instigated primarily by the Turkish state with the cross-border military incursions into Iraqi Kurdistan. If nothing else, the failure of the Turkish state to intervene against IS until the aftermath of Kobane shows that Turkey feared a stronger Kurdish quasi-state more than it did Islamic State, even when in the middle of a peace process with the former.
The small scale attacks during the ceasefire never lead to deaths on either side as far as I know. So there was never a legitimate reason to break the ceasefire for either party. In 2015 Turkey took action in Iraq AFTER they killed the Turkish officers. So it is pretty obvious to me the PKK instigated the conflict in 2015.
It is true that Turkey preferred watching PKK and IS fight each other in Kobane in 2014 rather than support the PKK. And honestly I don't see anything wrong with that. The PKK was a far bigger threat for Turkey at that point. Just because they were in the process of peacemaking doesn't mean Turkey is obliged to help them. Especially not when it is easy to tell that Kobane is of strategic importance for the PKK. Why else would the Kurds make so much noise about saving Kobane while being silent about other similar Kurdish towns falling in the hands of IS? The PKK wants to use Kobane to smuggle their fighters and weapons into Turkey. Makes perfect sense why Turkey feared the PKK more than IS at that time. Even more so when you take history into account.
Anyway, it doesn't really matter who started what and why. A solution is what matters. I support the idea of an autonomous Kurdish state. At the same time Turkey needs to expand the rights of its Kurdish citizens. The only real thing preventing this from happening seems to be Turkey's fear of the PKK wanting more than that: Turkish soil. That's where things get complicated...