I agree, 15 - 25 passes on your strop is not enough... I make at least 150 - 200 passes before a shave. This maybe excessive, but it has now become habit. I myself have been straight shaving for 5 - 6 months. Like you, my first shaves were good. However the one thing I didn't have was consistency. It wasn't until my 3rd month that I felt each shave would go flawlessly. My point is that although I stared great, my learning curve only began to start from my 8th shave onwards and I felt like I had taken 5 steps back at that point... Of course your recent experience could be the result of not enough time spent at the strop. Best advise is to strop for 10 minutes while concentrating on your technique. As your technique improves that 10 minutes will be halved and so on... Good luck.