Lisa took 10 x 3 = <<10*3=30>>30 photos of flowers.
She took 30 - 10 = <<30-10=20>>20 photos of the scenery.
So, Lisa took 10 + 30 + 20 = <<10+30+20=60>>60 photos this week.
Therefore, Lisa took 60 - 15 = <<60-15=45>>45 photos last weekend.
#### 45