The blue line is a week average and its up by ~15% compared to last change.
Its clearly going up.
Things are definitely going up. There's a steady baseline trend of about 2% to 2.5% per difficulty change. The one before last looks like an overshoot, the last one was an undershoot and both are well within a pretty normal statistical range over a 2 week period. The upwards trend makes sense as older equipment will be steadily replaced by large miners.
I'm unsure how you've estimated a 15% change though? The current difficulty is 41.2B and the peak I can see for the blue line was about 45.3B (it's fallen back a little since then) which would be ~10%, but the blue trend isn't much higher than it was in the middle of the last difficulty window where it was up around 43.8B, and that's only 3.4% higher than the recent peak.
If you look at the daily stats there' nothing very interesting about the last few days: https://blockchain.info/charts/hash-rate?showDataPoints=false&show_header=true&daysAverageString=1×pan=&scale=1&address=
The most interesting thing is a few days of bad luck just over a week ago and one day of very bad luck on the 13th, both of which depressed the numbers on the last difficulty change.