I want to overclock my inspiron 15 cpu.Recommend a good overclock software.?

Software?

What you don't understand, is that when you see a friend using some program on their desktop to overclock their computer, that program came with their motherboard... and communicates DIRECTLY with the motherboard to adjust the same settings you could go into the BIOS and manually adjust. That's right. You need a motherboard that allows you to change settings like the system multiplier, core voltage, cpu frequency, etc. This is why not every desktop computer can be overclocked. Not every desktop motherboard allows you to change these settings.

Yes. I know you are asking about a laptop, and not a desktop... but I'm getting to that.

Do you know what happens when you overclock a computer? The processor runs hotter than it is intended to run. This is why Overclocking voids warranties. With a desktop computer, enthusiasts can add aftermarket cooling products to help the OC'ed processor run cooler... larger air cooled heat sinks, multiple fan coolers, peltier chip coolers, water cooling rigs. These things are necessary, as the stock cooling that is included with a computer is sufficient to remove the heat generated by a processor running as it was designed to run.

Exactly how do you intend to increase the cooling capacity of your mobile processor, if you were able to overclock it? A Chill Pad isn't going to do it, because the processor is STILL going to be getting hotter than it is supposed to, which will trip the auto shutdown feature, which will in turn make your laptop unusable before you even get to put it on the Chill Pad. Laptop manufacturers know this, which is why they don't include BIOS settings to even allow you to overclock the mobile processor.

The short answer is that you cannot overclock your Inspiron 15, because Dell did not build it to allow you to be able to overclock it.