Snapdragon 410 is a quad cortex A53 processor whereas Snapdragon 400 is a old quad cortex A7 processor. Snapdragon 410 has high performance, power management, thermal output efficiency than Snapdragon 400. Snapdragon 410 has LTE by default on it, has new Adreno 405 GPU. Snapdragon 410 has new IZAT C GPS. These are the improvements of Snapdragon 410 over Snapdragon 400 processor, As well Snapdragon 400 is over 2 year old processor whereas Snapdragon 410 processor is out in the market only about 10- 12 months.
Snapdragon 615 processor is not comparable to Snapdragon 8** series processor. For example The Antutu benchmark comparison of Snapdragon 615 and 801 processor is as follows:
Antutu V5 benchmark:
For Snapdragon 801
Average: 42120.8 points (58%)
Minimum: 36792 points
Maximum: 47123 Points
Median: 41937 points
For Snapdragon 615
Average: 35815.7 points (50%)
Minimum: 27825 points
Maximum: 49293 points
Median: 30329 points
Snapdragon 615 processor is a year old processor and always the Lumia devices have used old processors in 7**, 8**, 9** series Lumia Smartphones after 720, 820, 920/925 Lumia Phones. Why they( Now, Microsoft Mobile ) can't use latest processors and people simply love the newest more? There are also news in the web that snapdragon 615 processor heats a lot and there is no news about quad core snapdragon 610 processor and by the fall of this year, snapdragon 620 processor would be out in the market.