Are there any instances of the PKK targeting civilians during the insurgency of 2015-present?
Mostly no, not by themselves. On the other hand, there's a big debate whether the newly sprung TAK (Kurdistan Freedom Falcons), which has engaged in bombing of civilians in Turkey at large, is really unconnected to the PKK. The PKK says so, but (e.g.) the Obama administration thought otherwise, e.g. in a 2016 press statement they said:
We also condemn the senseless motorcycle bomb attack near a police station in Istanbul on Thursday that was claimed by the Kurdistan Freedom Falcons, the PKK's urban terrorist unit.
Regarding PKK itself, I can think of the 2016 Dürümlü bombing. The PKK has defended this attack as a legitimate/non-civilian target:
‘Who got killed there? They say they were civilians, right?’ Bayik grabs his own guerrilla uniform firmly, and says: ‘If I change these clothes for civilian clothes, would that make me a civilian? No it would not.’ He means to say the people who died in the explosion in Dürümlü were in fact so-called village guards, Kurds paid and armed by the state to help in the war against the PKK.
Officially the PKK/Bayik condemns attacks against civilians.