First of all, the Turks have already invaded Iraqi Kurdistan many times, in the 1990s and after, and they have nothing to show for it. Their latest attempt was in February of this year, when they claimed a great victory but in fact were quite humiliated by opposing PKK forces. At one point in the 1990s even Barzani's peshmergas went up against the PKK, in collusion with the Turks, but they got nowhere. Believe me, the war is futile and unwinnable, and the Turks' threats to invade Iraqi Kurdistan are meaningless.
Second, these casualty figures are not "relatively small," especially since Turkish officials have been saying for a long time that the PKK is "strained to the breaking point," and is "on the verge of collapse." Fifteen is a lot of soldiers to lose when you've been hearing this kind of nonsense. Also, the number fifteen is probably a lie. The PKK claimed 65 killed, but they can't verify that either. The point is, it was a powerful attack conducted by a group that the Turkish Army is always on the verge of defeating. If you read the PKK website, you would see that they regularly are graduating new classes of recruits from their training academy in the mountains. Read my past posts here or at pashagypsy.blogspot.com for more info.
Third, and this relates to #1 above, you have to know which part of Iraqi Kurdistan you are talking about. Most Turkish forays have been into the mountains near the town of Cukurca, close to the Iranian border. Conventional equipment--tanks, trucks, jeeps--is useless in this terrain. Further west, the main entrance from Turkey to Iraq is at the Habur border crossing, where the Habur river joins the Tigris. Yes, tanks could cross the bridge there, but the Iraqi Kurds would almost certainly resist and dynamite the bridge. And invading there would do NOTHING to harm the PKK, who hold the ground far away from there, in the mountains to the east.
Fourth, the latest attack is causing an uproar because this particular army outpost, Bezele, has already been attacked, with devastating results, in May of this year. For more on this, you really should read Mizgin's post (rastibini.blogspot.com) and click on the link to the video of the May attack. The outpost is very poorly situated, and the Turkish boys who were killed there were in effect sacrificed to incompetence. The video does more than anything to show what the PKK looks like: the "boys and girls" marching together through the mountains, the pack mules they use, the weapons they carry, the awesome terrain, and finally the attack on Bezele, deep in its valley.
Next, is the vaunted Turkish Army a "paper tiger"? Well, I'm no military expert, but you have to remember that the vast majority of this huge force is composed of draftees serving their required 15 months of national service. I repeat: FIFTEEN MONTHS. How much desire and experience are you likely to find in draftees that are only in there for 15 months? Remember, these are not the "Turks" of popular caricature, storming the gates of Vienna with daggers in their teeth. They are ordinary kids (and many, remember, are Kurds!) who want to get back to their jobs, education, wives, etc. Some, of course, are far-right fascist jingoists, but those guys are always around.
Last, of course the PKK is bitterly despised by a lot of Turks, especially among the common folk whose sons bear the lion's share of the burden. (No offspring of politicians or army generals has yet been harmed--or even served!--in this dirty war.) Among Turkey's Kurds, however, the PKK gets a lot of respect and support. When PKK fighters die in battle, their bodies are collected by the Turkish Army and returned to their parents. (Sometimes, as recently happened with a boy and a girl, after having been dismembered by the Turks.) It is quite common to see photographs posted online of the burials of these "martyrs," and always the bodies are accompanied to their graves by thousands of people. As for Ocalan, he is a figurehead, safely ensconced in his jail cell and occasionally visited by his lawyers. He was never a real military commander anyway.
I hope this makes some kind of sense. Honestly, and I say this in all sincerity, I don't blame anyone who throws his hands in the air and walks away from this subject.